I'm planning to buy a yoga mat for myself tomorrow (YAY PAYDAY!) but there are a bunch of different ones, and I'm confused as to what makes a "good" yoga mat. I've seen some at Walmart that...well, to be honest, they don't look like much. I mean, I look at them and think, "Well, I'd be just as well off lying on the bare floor." They're really thin and don't look like they would make any difference whatsoever. (Of course, they're only, like, ten dollars.) Then there are ones that are $14.97 and ones that are $29.97. (Now, granted, the more expensive ones are Everlast brand, so maybe I'd only be paying for the name, idk.)
Anyway, long story short: What makes a good yoga mat? Is any old one good enough, or would I be better off paying the (slightly) higher price for the Everlast brand? Are there differences in thickness or whatever?