All three phones that you mention I own! And here's my take!
8700- Rock Solid, very reliable in all areas, great keyboard layout! However, it's a little out dated in my book. And I happen to be a big fan of the newer trackball!
8800- Work Horse in just about every area, fast downloads, unbelievable Screen color, real sexy looking device! But build quality has been the talk of town over the last couple of months (loose Rails)
and some people feel the keyboard is a little cramped.
Honestly, the keyboard never bothered me! I got used to it in no time.
Curve- unbelievable Form Factor, second to none in the PDA world right now when you talk about size and weight. Very comfortable keyboard, not as big a layout as an 8700, but very easy to type on. Decent camera on board, and pretty solid when you talk about build quality, way better then the 8800 series! Solid performer so far when you talk about speed, and probably the clearest and loudest blackberry to date. Some trouble with static was talked about with some units, but the one I have now is clear as a bell, and the speaker is nice and loud! Now since it's only been out about a week, the verdict is still not out for it being the king of the BB thrown! Some issues have been thrown out there ranging from OS Lag, slow trackball movement, slight creaks in the bottom of the unit, speaker phone issues, and static on the line! But, the one I have now (3rd one) is absolutely wonderful, none of the above issues! Guess I got a Gem, and I'm loving it so far! My advice is to give it a try, once you use it for a day you'll see just how much the Form Factor rules! Not to mention it's a great performer as well! Hope this helps, Good