Thanks everyone for the help! Here's the two bikes i'm interested in, but I have no idea how to size a mountain bike by looking at some pictures. I know with road bikes I can ball park the sizes, so i'm hoping someone can help me out here.

I guess I need about an 18-19 inch frame, but I can't really take any guesses since MTB geometry is so weird (to me).

Obviously the Giant is a little bigger of a frame, but is it too big? Or is the Diamondback small? I'm about 5'10 - 5'11, 170 pounds. Any chance either of these will fit? I definitely like the look of the Diamondback better, but it seems like a small little frame, probably too small for me?

And if so, which bike is the more quality bike (of it's time)?

http://sdrv.ms/SY2r4u

http://sdrv.ms/Wf3kEA

Thanks!

Hopefully those links work!