There are some significant differences between the 22, 23 and 25, but they are a "family" of boats with many similar design features. I am less familiar with the Oday 26, but it appears to be very similar to the 25, just with a more angular appearance. All are great first boats. There are also significant differences in features of each based on model years. Check out the I Heart Odays website for lots of detail.
I Heart O'Days