Depends on what you're into... if you want to race against others with boats like yours, find out what boats are around you. 99% going to be the Hobies, and more likely to be the 16 over the 18. If this is a boat just for fun or you don't mind racing on a handicap system, go for the best deal. All three boats you named have devoted followings, some more nostalgic than others.

Let us know what you get and how it goes! Good hunting!