I've had both the catit and the freshflow.
The catit was nice, because it had a big filling area (in my opinion). I had to fill it up every three days with my two cats. Pushy lady is right though, it does get empty faster during the winter. I did not like the filters on it, they had to be cleaned really often and the top was difficult to put back onto the bottom part most of the time. By the end it was also pretty loud, because the spring that lets the water loose wouldn't work and the pump was constantly searching for water.
I like my freshflow better. It's quiet, and easy to put the water into (no struggling to fit top to bottom). The filters are more efficient too. Taking it apart for cleaning can be a hassle, but I find it gets easier as you do it because the plastic gets used to being taken apart and put back together. I have a medium sized one, and I would say for sure to try to get a large one (I think they have them for dogs too). I need to fill up my canister every day or every other day with 2 cats. Really wouldn't want to see the small one!
The new platinum drinkwells intrigue me, but I don't think I'd like the sound of the water running 24/7 and they're more expensive. They do have the extra sized canisters though, if that's a big concern.
Hope that helps, I know I'm saying some stuff the other folks said, but it helps to have more than one opinion