What is the best mountain bike for less than $500?

I've been looking at the Trek 3700 and 3900. I'm not new to biking, but I'm just 15 trying to get a new one for Christmas (some dude totalled my old one when it was locked in a parking lot >:( ). I'll only be doing real hilly rides maybe once or twice a month, so I don't need anything that's like God-strength.

Also, I've grown about 3 inches since I've riden my last bike...I'm 6'1" is a 19.5" bike good for my size? Or should I go bigger or smaller?

THANKS!
 
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