Which type of punching bag should I get?

In order of importance:

1.) Heavy bag

2.) Double-end bag

3.) Speed bag

4.) Slip bag

In my case and in any other case where a style emphasizes on a lot of head movement, I would move the slip bag to number two, but in any average Joe's case, that's how the list plays out.

Onto the heavy bag decision, it's common to get one at least half your body weight to start out on. If you're not rich, I would opt for one that's a little more than your body weight, considering you'll likely never buy another heavy bag. Bag weight plays a considerate roll in developing power. Consider that Marciano and Tyson got their power from training on 300 pound heavy bags (Tyson, once a 350 pound heavy bag). But to just stay in shape like you said, just buy one that's 70-100 pounds (or half your body weight).

I've stated before that the only brand I really trust or recommend when it comes to heavy bags is Ringside. They're the highest end of quality on the reasonable price scale. That being said, I personally think their water/foam heavy bags are the best bet because they're easier on the joints and they can also be drained and the weight customized. Whatever you do, steer clear of Everlast, Title, TKO, Lonsdale, and really any other heavy bag maker that isn't Ringside. I'd also recommend Grant and Cleto Reyes brand heavy bags, but they are horridly overpriced. That's about all I can say. Hope I helped.

a heavy bag would be good for the workouts your doing just now.great for when stressed too.ive got 1 in my garden great workout.