I've only stayed at the Cosmo from those three choices, but have stayed twice. I thought it was great, very flashy/hip, seems to be for a younger crowd, but either way very cool (I was 26 the last time there).
Awesome pool that overlooks the strip, complete with outdoor ping pong/pool tables myself and wife enjoyed. It'll be too cold, probably, to get in the water, but nice either way.
Great buffet, I haven't been to many Vegas buffet's but it was the kind of place you take pictures of your food, and I'm not at all into that on a normal basis. Very diverse menu too, from classics, to bone marrow! Not that I liked it, but cool to try new food. The food was all very small portions as well, so you can try a ton of different items.
Great location, although you already know that.
Table game limits were higher than other casinos, granted I was mainly at Bill's, Flamingo, etc.
"Hidden" pizza place, well worth the find.
All in all I was very happy with our stays there. But from reputation, I'm thinking any of your choices will be great!
Also, have you considered off the strip? I've stayed at the El Cortez cabana suites, cheap, but nice. Save more money for gambling/losing!