That really depends. Most of the quiet pools are often very quiet at the WDW hotels. Not exciting, but you often have the whole pool to yourself. On a cold winter day, all the pools are pretty empty. On summer days, they can all be relatively crowded. Some like the BC/YC pool is both crowded (in some areas) but also has quieter/less crowded areas.
One that is consistently pretty quiet is the quiet pool at the Contemporary. It is within sight of main pool, but always relaxing with a view of the lake.
I have not been there in some time, but the Boardwalk quiet pool has a hot tub, and has gardens, and was very nice.
A mina pool that often has plenty of space is the one at Swan/Dolphin. You can easily move between the quiet/main pool if you want more room.
WL has one of the most crowded/cramped main pools. AKL and Poly are pretty crowded at the main pools.
Many offsite pools are pretty quiet, but many are not all that exciting. A large pool complex just off WDW with lots of slides/features is the Marriott World Center.
Oh, one more option - if you are going that way - are the onsite Universal pools. Portofino has multiple pools, and plenty of room to spread out. HRH has live music. Sapphire Falls also has a great pool that is both fun and has some quieter nooks/plenty of room.