You’d actually be surprised how fast those little legs can move! I have a dachshund at my parents house (hes actually trying to join the laptop in my lap right now) and when he was younger he lived for his walks and playtimes with my sister and I. They are nowhere near as active as dogs such as labs, but while young they do need a bit of play time. They don’t make good jogging partners, but in shape dogs are great for powerwalking/walking long distances. IMHO, I would have one as a single person, but they really would prefer another animal (dog/cat/human) with them.
My grandma had a chihuahua/dachsund mix. I doubt she ever took her dog for a walk, and it was an active dog, but just running about the house was probably enough exercise for that one. 
My (adult) daughter has three chihuahuas. They get plenty of exercise just worrying about everything. Wierd pooches. But endearing. 
mangeorge
I lived alone in a condo with a dog, and while it is do-able I did feel incredibly guilty having to go and work for 9 hours a day. My dog was fine, but I felt bad leaving him alone for so long. I also had cats, so he wasn’t totally alone, but I still felt bad and spent nearly every other waking minute with him to make up for the time I had to leave him.
Dogs are a bg commitment, so think it through thouroughly. You need to have a back-up plan of who will take care of your dog if you can’t. For example, I got so sick one time I could barely walk, yet my dog still had to go out. Luckily my BF could come over to do it. If you go away over the weekend or even overnight, you need to either take your dog somewhere to get cared for or have someone come in.
I agree with the older dog idea - a puppy would not be suitable for a single person. They require too much time and attention. During house training I took my puppy out every 2 hours around the clock.
I live in an apartment with two dogs: a Collie and a Rat Terrier mix. Both do reasonably well in the apartment if I walk them often enough. I usually do 4 walks a day, average 15 minutes each.
Day care is available in some places, but the closest one to me is further than my office so it’s easier to come home during lunch than take the dogs to day care every day. If I’m away all day or evening I use a pet sitter - she has my apartment key so all I need to do is make a phone call and leave a $25 check. (That’s for 2 dogs. I think it’s about $17 for one.) For overnight and longer trips I need to get them boarded - about $25/day/dog. That means I often pay more for their boarding than my motel room.
I have a webcam at home so I can keep my eyes on my dogs during the day. They spend almost all the time sleeping their favorite spots, so I don’t feel too bad about leaving them alone.
As I’m sure you realize, it’s a long-term commitment. You can’t dump them even if your living conditions change (e.g. get a job in a big city, or want to move in with an SO who has 2 cats), or if they get sick. One of mine has epilepsy, and it’s not an insignificant emotional strain for me. Financial strain too - a visit to the emergency vet can easily cost $400. (Basic exam is about $70 but then there’s blood tests, IV drips, medication, overnight stay, etc. But the good news is that there are emergency animal clinics, open all night and all weekend.)
If I had to recommend one breed over the other, I’d say the rat terrier is much easier to take care of. You don’t need to do much grooming, and a bath takes no time. He’s very smart, though that’s not necessarily a good thing - he can open the kitchen cabinet and get at the garbage can, and he hasn’t fallen for the “throw some hot peppers in the garbage to give him a lesson” trick - he just avoids the peppers. But a simple child-proof latch ($3 from Toys-R-Us) solved this problem. I think small size is a definite advantage - it means smaller crates, smaller beds, slightly cheaper cost for boarding and medication, slightly longer life expectancy, etc.
I highly recommend this book for choosing a dog. It doesn’t have every breed, and can’t help with Humaine Society Specials*. What it tells you is that you do not want a Golden Retriever (it’d go insane alone).
<shameless plug>
Get a Shiba Inu. They’re small, cute, independant, and very loyal. Plus, they’re a girl-magnet on walks.
</sp>
*:Let the dog pick you. (kinda like in Soviet Russia)
I live alone and my dog is pretty great. How I picked her is, I went to the SPCA and went in to see a dog that was not running around like a maniac, barking her head off. She was calmly sitting in her room, looking at me. When I went in to see her, she came over and sat in front of me, then lay right in my lap. That’s when I knew. She has a very easy-going temperament, is fine with the cats and home alone, and is overall not a very taxing companion.
You may want to consider volunteering at the Humane Society. I walk dogs there a few times a week. They get badly-needed attention and I get the fun of a dog without the responsibility.
It has the added benefit that when I am in a place where I can adopt a dog I’ll know which one to get - I’ve had experience with all sorts of breeds now.
Breeds:
stay away from Border Collies, Blue Heelers, or any other “working” dogs. They will go insane by themselves and redecorate your living room.
Rescued greyhounds are IMO the best breed for a single working person. They are the biggest couch potatoes in the canine kingdom. They love to lay on a soft cushion all day, then romp for 20 minutes in the backyard with you at night. Rescues can have some separation anxiety issues, so it is important to learn a bit of obedience training (for you more than the dog).
That is very unusual. One of the vets that volunteers at the local Humane Society told me that a dog’s stress level is at 90% the entire time they are in the shelter. Easily 80% of the dogs I walk calm down the second they get beyond the shelter doors.
I may have already missed someone else asking this, but have you thought about getting two dogs?
This will go some way to combating the loneliness aspect.
I had a similar experience with my dog, who was a shelter dog. All the others were going crazy, and she was just sat there, looking at me. When they let her out of the pen, she jumped at me and gave me this look of “c’mon then, take me home - I’ve been waiting ages”, and that was it.
Of course, when I got her home, she displayed classic seperation anxiety symptoms, and I spent 6 months persuading her that whenever I went out, I would always come back, and she really didn’t need to chew up all my possessions to ensure my safe return. 
If you want to be a good parent, you’ll have to schedule your life around them (single or not). They have to be walked, fed, and you really have to hang around with them. My BIL leaves work to walk his dog or has his mother do it. You really need to evaluate your ability to be there when they need you.
Cats, on the other hand, can go longer periods of time without seeing you. You can go out for the weekend and they’ll be fine if you leave them enough food, water, and clean litter.
Even though you can’t take a cat to the lake to play throw the stick, they’re still very affectionate buddies when you’re home.
I wouldn’t leave a dog alone for that long because it would get lonely, but you can litter-box train dogs, too.
A friend of mine had two small dogs. She bought a large litter pan and filled it every day with shredded newspaper. When she came home from work, she would dump the pan into a large trashcan on her back porch.
She said it was easy to train them. Whenever she caught them starting to squat, she would just pop them into the pan, and then praise them when they went.
Yeah…my friend wants to get a tiny little dog and litter train it. But they need different emotional support than cats do. I couldn’t leave a dog, either.
She had two dogs, so she didn’t feel as guilty about leaving them alone during the day, because they provided companionship for each other. Regardless, I would never leave a dog home alone for more than twelve hours, even if it had a doggie door or a litter box. Lonely dogs can be destructive or get depressed if seperated from its pack for long periods of time.
Most dogs are okay with the seperation that comes with a normal eight-hour workday. Most of them use the time for sleeping, and they get used to the schedule. (My dogs go downstairs at about 4:30 to wait for my husband who comes home about that time.) It’s best to give them something to do during that time until they get used to it. I like to fill a rubber Kong toy with peanut butter and freeze it overnight. It provides hours of yummy fun.
My grandma recently got a dog and is having some problems with it. The dog had previously belonged to an owner who was gone up to fourteen hours a day, and kept the dog confined in a small crate when she wasn’t home. The dog soils its bedding (grandma crates it overnight) and when out of the cage, runs frantically around the house and in and out its doggie door. I told grandma that these behaviors will stop once the dog learns that it gets let out in the morning and doesn’t need to pee in its bed, and once it gets used to having all of the space, it will calm down.
Is PB okay for a dog? My old Julie loved it, even though she knew how silly she looked eating it. I think most dogs like it.
Everything in moderation, I’ll bet.
mangeorge
Oh, yeah, peanut butter is great for dogs! It’s got lots of protein, and I’ve never met a dog who didn’t go nuts for the taste.
I use it to stuff rubber Kong toys. Freeze it overnight, and the dog will have fun for hours. You can also use it for disguising pills. And a friend of mine smears some on her refrigerator door when it’s time to clip the dog’s nails to distract him.
Good. It’s a lot of fun to feed it to them, and they sure do love it.
Talk about bonding.