It's all a matter of personal taste,
but since you asked, here's my take on the two:While I have never sailed on the O'day 25, I own a 23, and she is tender; significantly more tender than the Catalina 25. Since the O'day 25 is just a slightly bigger version of the 23, I would be willing to bet that the 25 is also a tender sailer, and more tender than the Catalina.A good generalization is that that a boat that carries its ballast lower will be less tender. The Catalina carries its ballast in the fin way lower than the O'day, which carries virtually all of the ballast and righting movement in the centerboard trunk/keel. Since I have never sailed on the O'day 25, I can't really say for sure which one will point higher or go faster; but, I own an O'day 23, and have sailed extensively on both the Catalina 22 and 25. There are so many variables, not the least of which is the skill of the crew; however, the boats all share a common design style (canoe bottom, transom-mounted balanced rudder, relatively wide beam), so I think it is fair to assume that all other things are at least relatively equal between the O'day and the Catalina; the major difference is the fin keel vs. the keel/centerboard. You may get some other opinions by those who have actually compared the two, but I would be willing to bet that the Catalina 25 is a stiffer, more stable boat than the O'day 25, which generally translates into greater speed and pointing ability. I have sailed both the centerboard and fin versions of the Catalina 22, and the fin version was noticably stiffer, faster and higher pointing. Downwind, I think the O'day would have an advantage; you can retract the centerboard, which does add to your speed. I know you didn't ask, but one thing that would make it easier for me to decide would be to also consider the other features of the boat. If you are planning to weekend or cruise at all, the Catalina has (or most of them anyway) a pop-top. This is a great feature that really enhances the livability on board. Almost made me bust my budget and buy the Catalina over the O'day 23.