Encore Beach Club is my favorite pool party in vegas for many reasons.
Not only is the pool cleaner than most in Vegas, the people are cleaner. The crowd at Encore Beach was awesome (good looking but most very friendly). I went on a Sunday for Daystars Calvin Harris and reserved a lilypad in the water for a $500 minimum. It helps to have a promoter set this up or they will try and charge you $1000. I advice you to spend the 500 on a bottle rather than mixed drinks, which are usually very watered down. With the bottle purchase you get a ton of mixers. You also have a personal waitress and pool attendant. Very luxurious.
Calvin Harris was great as was the set up of the pool area. It never seemed too crowded and the energy felt right the whole day into the night. I would advise coming early and buying tickets ahead of time if you do not plan on purchasing a daybed/lilypad or a cabana (which are pricey)
Its a much more intimate experience than Rehab or Wet Republic but the opposite of TAO Beach, which I find dirty, cramped, and too loud. Everything at EBC is great...even the BBQ chicken wrap!