I think WendyC is pushing her own place and her own little piece of Belize ... too bad she has to put down other businesses and Ambergris Caye. Marty is a nice guy, so he won't, but a lot of other Web site operators would kick Wendy off the board.
As to your question, I think any of the four you've chosen would probably fill your bill. I've stayed at only two of them, Captain Morgan's and Victoria House, but I've visited and toured the other two several times.
I personally would rate the four places in this order, but they're all pretty close:
1) Victoria House (but the units here vary from deluxe to somewhat ordinary)
2) Banyan Bay (all the units are nice two-bedroom units)
3) Captain Morgan's (some condo units, some cabanas)
4) Caribe Island (a variety of units)
Actually, Victoria House does have suites with kitchens, but those are only the owners suites, which are quite expensive.
As to the beaches, I'd probably give Mar de Tumbo at Banyan Bay the top nod, but no one beach stands out. I'd personally give the beach at Captain Morgan's the lowest rating, but others might differ.
All have pools. Not sure that one or another would be better for couples.