The 27/28 will have more room and amenities than the 24, which can be quite spartan in some versions. Some 24's have heads, mine does not. The flip side is weight, you will need a more capable vehicle to tow a 27/28.
Newer versions will have performance improvements such as a rotating
mast.
The oldest 24's (Mk1) have a
centerboard rather than daggerboard, and while a little slower, are better suited to cruising. The 24 Mk2 added rotating
mast, and went to a daggerboard. The Dash 750 had a taller rig and bigger amas which give it better performance.
The 28 improved on the 27 with among other things, a rotating mast, and added an aft-cockpit version.
Corsairs are well made, extremely fast and fun
boats. For single-handing, you'll probably want a small tiller pilot. Not hard to launch with a little practice, especially the 24'.
There's a really good
Corsair owners group at
https://fct.groups.io/g/main