First of all, CTB is the only one with good advice.
#1. Ra at the Luxor is dead. Gone, out of business, finished.
#2. OPM has the rep with the locals as the most "ghetto" club on the strip. The crowd is a bit hostile compared to the other clubs, there generally seem to be more fights and girls get groped a lot more there than elsewhere.
#3. Studio 54 is for the over 30 crowd. If you want young, do NOT go there.
Where should you check out?
Tao (at the Venetian), Body English (at the hard rock), Tryst, Rain (at the Palms), Pure (Ceasars palace), etc.
To get a good idea of what crowds are like at specific clubs, check out
http://vegas.napkinnights.com/. Cheers!