Not sure if it's changed, but Oyster was historically known for really detailed Vegas hotel reviews. They'd surely have a list of best hotel pools.

https://www.oyster.com/las-vegas/hotels/

You can also get some decent mileage out of Booking.com and checking reviews for keywords. That won't help you quickly find the best hotel pool, but it will help you find out what people think of a specific hotel's pool (e.g., Circus Circus).