Re: What kind of punchbag do you's recommend?
I'd pick a hanging bag over any other kind any day. However, due to your problem, I can't be too sure. Whichever bag you choose will get messed up pretty quickly from being outside. You could always take the hanging bag off the bracket and bring it inside when you are done, but you're right about the rusting bracket (I'm assuming theres no way you could put a small roof over it or something...also assuming a tarp would help, but only delay the inevitable).
I can't stand standing bags (wavemaster). It doesnt swing, so you cant work your timing, and they seem to fall over far too often.
The torso thing is okay for working on precision strikes with many martial arts, but not terribly useful as it has the same problems as the standing bag, PLUS the fact that you cant really work on your footwork very well (as you can really only hit it from the one angle).
Boxing is like a handjob, and MMA is like a hot sweaty orgy with 5 chicks. I could never say no to a handjob, but which would you rather have?