Troy,
I have never flown a Trex. I do own a B400. There are pluses and minuses with it. In my view, it is a very good heli to learn more then just hovering. It is capable of loops, rolls, stall turns, and other basic manoevurs (sp?) in stock configuration. I have done these with my stock B400 Upon my first crash, I replaced the servos with HS65's. The stock servos are a weak link. I find the stock gyro to be acceptable but will upgrade it as i progress. The rest of the heli is very solid too. Right now you can pick up a B400 RTF for $370 off of a reputable dealer on ebay. Add another $75 for good servos and for about $450 you will have a VERY nice heli. That's not to say a Trex isn't capable. It's more a matter of your budget.
Hers a link to a video I did with stock servos. The only thing non stock is the landing skids.
http://www.youtube.com/watch?v=7XAQFmOIRGw
The B400 I believe is cheaper to repair on a crash because you are replacing plastic parts instead of metal ones. But remember, the aluminum Trex parts are what makes it such a good flying heli. Research both and let your budget be your guide.
Jim