With the biggest beach in town at 11 acres, our first choice would be Mandalay Bay's but unfortunately it's closed this winter. The good news is that it'll be back better (and possibly bigger?) than ever this spring.
The Hard Rock Hotel, above, has a crazy albeit young beach scene with the daily Rehab party and fun Tahitian cabanas.
The Encore's pool (pictured above) may be lacking sand but it has plenty of French Riviera- inspired style and its price point encourages a slightly more mature crowd. Look for the cabana package that includes a guest suite and cabana each day starting at $600 with code WUCAB.
Tao Beach at the Venetian is an extension of the huge nightclub with daytime parties featuring well known DJ's.