You'll also want to consider your intended use case carefully. The C25 is a good "trailer sailer". It takes a while to set up (raising the mast, etc. can easily take an hour or more), but the beauty of the 25 is that it is light enough to be towed by a decent-sized SUV, especially for short distances. The wing and swing keel versions make trailering even easier. By contrast, the 27 is harder to trailer with more conventional "home" equipment. You're getting into the dual-axle pick-up or commercial vehicle territory. On the plus side, the 27 has more room. It's a more comfortable boat all around. That's not to say that the 25 is uncomfortable, but the 27 is more comfortable. Kind of like moving from a Honda Civic to a Honda Accord.
Alex and I disagree on the C30. For my purposes, it would be a good boat. Nice, wide beam, and lots of room below for my family to play and spread out, and a nice size cockpit for the family, too. It's not a fast boat, but for my purposes, I'm looking more for comfort over speed (that's why I wound up choosing the Allmand). Continuing the analogy above, the C30 would be like moving to a Honda Pilot from the Accord or Civic. But the C30 weighs SIGNIFICANTLY more than the 25 or 27. That means it takes more air to get her moving, and more power to get her to stop. With the 25, we were able to control her movements pretty easily through brute strength. With the heavier boats, you have to watch because inertia can be a real issue.
Some big advantages of the Catalinas is that the company is still in business, there are still parts available directly from Catalina, and, due to the huge number of boats the company built, there are many aftermarket suppliers of parts.
As I recall, I believe there are several Catalina 25 owners on Lake Texoma. You can check out Catalina - Capri - 25s International Association
to get more specific information on the C25's, and they will likely also be able to give you good marina recommendations.