I've never stayed at Cypress Harbor, but have stayed at Harbor Lake a couple of time, and absolutely loved it! Of all the Marriott condos I've stayed at, it's pretty much one of my favorite (like, it has a REAL pantry area for groceries, yes it's the small things that make me happy!). We stayed there last time for a Sea World/Discovery Cove trip, and it's super duper close (okay, I'm sure you know Cypress Harbor is just across the street).
Harbor Lake is a much smaller resort. For your kids' ages, the pool is great - lots of water play fun time. I know Cypress Harbor must have a great pool area (or multiple) as well, but didn't stay there. I just loved how small and safe Harbor Lake felt - everything is really close. I would order sandwiches from the bar area to go, and just run down when they were ready (the night I was lazy and we just wanted to relax).
The second bedroom in Harbor Lake had two queen beds. That is one reason I would pick it over Cypress Harbor. The second bedroom setup is different there - a bed and I think a sofa sleeper or something? I wanted a bed for each of my kids - I heard with the sofa sleeper opened there is little room to walk around in the second bedroom. Just go to Marriott Vacation Club website and you can see the room floor plans - that would be a good way to decide which works for you. You can also do a virtual room tour - very cool.
I always requested a high floor at Harbor Lake, and got it - it was nice and quiet!