Went to store for a new plunger. There are so many. Almost flat type, A small bellows type, a long bellows and some that shoot air into pipes. Which is best.? Should plunging be done occasionally to prevent or do you wait until you need it.?
Is there a recommended drain opener? Is liquid better that granular?etc.
Should drain openers be used as maintenance?
This picture shows three common plunger types. The black one with the bellows does a better job than the other two.
Occasional plunging anytime the sink drain is slow is actually better than waiting for a complete clog.
As far as drain cleaner go; I have to first ask if you are on a sewer system or septic? If septic avoid using drain cleaners. Drain cleaners are very harsh on septic system.
Even if you are on a sewer system, you should use drain cleaners sparingly. There are a few rare problems with drain cleaners. They can break down soap deposits that are preventing small leaks, occasionally they can damage plastic drain fittings and worst case scenario is my brother-in-law once got a small explosion that caused drain cleaner and grease to shoot back up out of the drain. I have no idea what caused the reaction, but my BIL suspected the people had dumped baking soda down the drain before he got there. He was okay thankfully.
Jim
I saw one that injects air. Would that be dangerous?
This seems counterproductive to me. A plunger normally works by creating a partial vacuum in the drain line, pulling “backwards” (contrary to normal flow) on whatever has caused the clog, and hence freeing it from whatever it has snagged on. In many cases, this will permit it to continue on down the drain, allowing water to drain properly thereafter. Injecting air would increase rather than reduce pressure on the clog – which could, theoretically, push it past the choke point, but one would think that if that could be accomplished, water pressure from above would have already done so.
Drains are low-pressure piping and often put together in a slipshod fashion, where the person doing the work is happy if it doesn’t leak. Potentially a large increase in pressure could cause you much bigger problems than a clogged drain. I have never seen these air injector plungers, but I would be worried about them if they generated enough pressure to blow out a clog. This is in addition to Polycarp’s well founded worries.
Jim
Haven’t much to add here–I’m no plumbing expert!–but I think the injecting air type that’s being mentioned is this sort of thing:
http://ldrind.com/ProductImages/SellSheets300/BellowsPlunger.jpg
There was one on amazon that was similar, but the bellows was outrageously long. Dunno anything about 'em. Carry on!
Or perhaps this: Amazon.com
10:30 on a sunday night and I’m researching plungers! Time for bed. 
I am no expert, though I did do a lot of drains for HVAC work once upon a time. I piped, plungered and snaked many a drain.
My BIL is an expert professional plumber and he recommended the style plunger I pointed out above. I have no experience with the style plunger you are linking to, but I do not believe they would generate enough pressure to cause the potential harm I mentioned above. I do not trust the design to last very long or do a good job, but that is just my opinion and not based on any experience with the style shown. I do not think they would hurt the plumbing, but I also think the other style plunger would do a better job.
On preview, concerning your second link; it is possible that the “Compression Jet Plunger” that generates “Approximately 70 CUIN Air”, might be dangerous to the drainpipes. I will defer to someone that can translate that number into PSI.
Jim
“70 Cubic Inches,” perhaps?
Yes, but what is 70 Cubic inches in PSI? I do not know the conversion factor. Is there a conversion factor? I cannot make a semi-educated guess to the dangers of the device without working in units I am familiar with. It may be perfectly safe or it might exceed standard PSI for a sink drain.
Jim
I have the first one Lemur Catta linked to and it works far better than my old one (the saucer-shaped rubber type with a wooden handle), mainly because it has the little extension at the bottom and that fits into my low-flow toilet without slipping or spraying water. When I’ve used a plunger on the kitchen sink, the wide type was better for creating suction. In other words, I’ve found that the application has a lot to do with which type works best.
The accordion type is, however, far more difficult to clean effectively once the toilet is cleared - not a trivial matter when the clog was one of the more disgusting ones.
I second What Exit?'s recommendation on the plunger. The bellows type linked by Lemur Catta works better for toilets than sinks, at least in my experience. That bellows is tough to get to work on a sink clog, but does a great job on toilets.
As far as maintenance drain cleaning, in general avoid caustic drain cleaners. They can harm your plumbing, are hazardous to work with, and if they don’t clear the clog, which is often the case, they make your problem worse. Now you have a clogged drain full of lye making plunging or snaking kind of tricky.
For maintenance purposes, an enzymatic drain cleaner is safer and more effective way to keep your drains running. The enzymes effectively eat the hair, grease and general grunge that line the walls of your drain pipes which makes clogs less likely to occur in the first place. Just pour some down your drains every couple of months. Easy.