hahahahaha.Quit both bands and tell them you can't handle the pressure.
The girlfriend analogy is pretty close sometimes. Except with a band, it's like being in a relationship with three or four people at the same time on several different levels. Some things can be great and others make you want to focus on the great things. There are an infinite number of possibilities. Great musician/bad personality, Great personality/bad musician, Great musician and personality/crap schedule. And so on, and so on.
I say when you find good people, and you enjoy playing with them, go with that all the time. If I said that I would do a practice, I would do the practice for sure. I would keep an open mind, but I would be polite and honest with them about my situation. You may not have the time or desire to play in their band today, but somewhere down the road who knows. It is great to have good connections.
A little over a year ago I was in a similar boat. I had a couple of false starts with musicians that I didn't click with. But when I found the guys I play with now, I knew that it was what I was looking for. And now, with all the networking that musicians do between bands, it would be much easier to find people to play with if my band decided to hang it up. At least I wouldn't have to spin the roulette wheel that is Craig's List. lol.