I've stayed at both, but have not swam at either.
Obviously you know they are sister motels. They both, if memory serves, have the "put the keycard in the slot so the air conditioning will go on" thing, and they have similar furniture/room arrangements. That's all great.
But at Carousel, the shower flooded (I still don't know how, I had the curtain "stuck" to the wall as I generally do) all the way into the vanity area, right up to the carpet, and when I got out of the shower and was dealing with the flood, the smoke detector went off b/c of the steam from the shower. I could not reach the smoke detector, had to quickly dress and open the door to let the steam out.
Worse? This happened around midnight, and no one from the motel called to ask what was up, no one came looking around, nothing. I called down to let them know, and they said "oh yeah, I was wondering about that"...so they could hear it, they just didn't come to check it out. And this was on the day that the hotel in Vegas caught fire (early '08) so you'd think they would have been more concerned.
The breakfast was bad and started on the late side for getting to the parks nice and early.
YES it's nice and close.
Anabella...lovely! The employees made me feel welcome. Their lobby is lovely with comfy couches, and they didn't mind at all when DS and I sat there with our luggage for upwards of an hour waiting for my brother to pick us up. The first floor rooms have wood floors, which has changed my opinion of carpet in hotel rooms forever. The restaurant there was good, and they let DH get me a boozy beverage from their bar and walk it over to me (I thought I would have to go through room service and pay their markups).
Yes the walk is longer. But it's pretty. Leave Anabella, get to the crosswalk between Tiffys and Cocos, cross towards Paradise Pier Hotel/Grand Californian. Walk along the path on the right side of that street, which is actually a giant hidden Mickey if you look at google maps hybrid view. Then enter the Grand's big doors, turn to the left, go down a corridor, walk down the hallway , go out to the right at the sliding glass doors, follow the path along, and you'll come out about 3/4 of the way through DownTown Disney, where you can go to DL or DCA. So it's basically just a bit longer than if your'e staying at PPH.
Unless you have a car, they'd better provide a cab to get from Carousel to Anabella to use their pool! And also make sure they won't charge you for parking if you have a car when you want to use the A's pool.
I personally would probably stay at Anabella, just b/c it's so much nicer than the Carousel. To me, the walk would be worth it.