Just go buy it, try it out and see what you think. You can delete the app and be refunded your money. You get 1 day to trial out any app, if you don't like it then you get refunded. I have loved Better Keyboard, for me at least it doesn't kill my battery. It does run in the background, but my battery isn't affected.
I would say give it a try and then see what you think. I've tried the default keyboard, TouchPal, and Better Keyboard, and of those, Better Keyboard is the best and most customizable.
Don't count MyTouch out, its a great phone, you just need to set it to your liking and then it'll be the perfect phone, that does take some time, but its always possible.