Keep in mind that there are lots of variations of exercise. If feeling good mentally is a primary motivator for you to exercise, consider group classes like boot camp, kick boxing, BodyPump, etc. These group classes will give you both aerobic and strength benefits, and are also “fun” in their own way. The instructor provides guidance and motivation which helps you get a great workout that flies by.
I feel that these kinds of general fitness classes are the best kind of workouts for most people. The classes are designed by professionals to give you a good workout, and the instructor guides you in proper technique and form. I feel an average person will get a better quality workout in a group class rather than on their own. This is because most people are not educated in proper techniques or even have specific goals they want to achieve. And there’s also the motivation factor. Solo exercises like treadmills and weightlifting can get monotonous and people often give up unless they have specific goals. If you are training to be a better runner, then you will be motivated to spend an hour on the treadmill. But if you’re just wanting to get healthier, the treadmill might not give you the motivation you need to continue.
If you decide to take group classes, be sure you start out slow and careful. A common mistake newbies make is trying to go at top exertion from their first class, but they often aren’t in good enough shape yet. They see everyone else in the class and try to mimic their movements and pace, but those people have been taking the class for a very long time. So the first few classes you should do at a lower exertion level and be listening to your body. Gradually increase your exertion over each class depending on how you felt from the previous class. This will help you advance without injury.
And lastly, if you decide to do strength training, use a single reference book or use a trainer. Weightlifting is more of a technical kind of exercise and you’ll need to get several factors correct in order to see results. Asking on a message board can be good, but the advice won’t be consistent. Each of us have our own preferences about how to do strength training, and they might not all be in sync. It would be like getting advice on cooking from chefs of many different regions. Each chef will give advice based on their region, but you won’t get tasty food if you try to combine the advice together.