It's been a few years since I've stayed at Sapphire Falls. More recently I've done a couple of large family vacations to Cabana in the exterior family suites. Personally, I prefer SF just because it feels like the "nicer" property to me. I do recall the beds being nicer at SF and I love the SF pool the best out of any of the resorts. But CB is definitely nice for the space/cost factor when you're talking about family trips. I do think it might be a bit cramped in a SF room in comparison to CB. Maybe worth mentioning is that the standard SF rooms (I think) all have that sliding barn door for the bathroom door. (read: stink/sound aren't as masked as with a real door..) CB suites definitely have the overall bathroom advantage with the way their bathrooms are set up to accommodate 3 people getting ready at once.
I asked my husband what he thought someone in your position should do, and he voted Cabana Bay for the space consideration and also because "there's more stuff to do for kids/teenagers who want to wander on their own."
Something I'm always quick to point out with the CB exterior rooms is that you do have a lot more opportunity for bugs. I wasn't totally prepared for that the first trip I took, and had to rectify my family's sloppy eating habits quickly because some overnight leftovers resulted in tons of various insects the next morning. Maybe i've just been unlucky in that regard, but it's been true with every exterior room i've seen there. I see it as more of a Florida reality with that type of room rather than a knock against the hotel. Also, we went to CB last May and got rained on hard.. Having to walk/run in the rain to our room all the time was kind of a bummer. These things might not prove to be true for you or even matter much, but just some thoughts. In spite of those things, I still will go back to CB in an exterior room when I have to accommodate my family of smokers. If it's just a trip with my husband, we would do SF over CB.
My advice regardless is just to constantly check the AP rates. New rooms pop up and prices change all the time.