The Cat 250 looks to be a Mac 26 (original, not X or M) competitor, not a high tech
racer.
The water ballast allows you to get your
boat up and down a
ramp a lot more easily due to lower weight and
shallow draft (1' 8"), allows for a smaller car for towing, and allows for very shallow gunkholing or sailing in shallow areas.
On the other hand, lead is 11 times denser than water and is in the
keel under the boat as opposed to the water ballasted version where the ballast is in the
hull up high.
I've not sailed either the original Mac 26 or the Catalina
centerboard boats. I have been interested in trying one out though. So without having actually sailed one, I would say if keeping the boat on a
trailer and typically going sailing on nice days (defined as lower wind) is the priority, then
centerboard. If you're more interested in higher
wind and better windward performance then
keel.
Bill Lee wasn't impressed with the centerboard version's sailing characteristics.
Cruising World - Catalina 250
John