I would suggest Mandalay Bay. We have stayed at quite a few properties and we've stayed at Mandalay Bay at least the last four trips...

Pros:
> It has the best swimming pools hands down.
> Giant Wave pool.
> Has a "Lazy River" that you can use inner-tubes to float around on.
> You don't have to walk thru the casino to get to the room elevators. Room Elevators are extremely close to the front desk and front entrance.
> Room elevators also go straight to the lower level rear entrance where access to the pools are.
> Nice buffet.
> Has mono-rail that goes to Excalibur and Luxor.
> Awesome view of the strip.

Cons:
> At far end of strip. I would prefer to stay at a property in the middle of the strip.
> Higher priced than other properties on the strip.
> Inner-tube rental is expensive for the lazy river. (Something like $20 - $25 per tube per day). We pack our own and inflate them in our room. They have no problems with you bringing your own tube. (No rafts allowed, must be a tube type).

The pools are the main reason why we go back to this hotel. We usually spend every morning laying out at the pool for several hours just relaxing. Also room access is the best I've seen. (Nothing like MGM where you need to pack a sack lunch before you attempt to find your room).