As long as the Prindle 18 is in OK shape, its a no-brainer. They're a great boat, not the most modern but still fun to sail, simple and pretty fast. Pretty much perfect for a novice.

The P-Cat might be reasonable if you were planning to leave it at a Yacht Club or marina, but it's HEAVY and slow. Might as well get a monohull.

The Sol Cat wouldn't be terrible but there's bound to better things for sale in your area if you wait. Like a Prindle 18, Nacra 5.7 or even Hobie 18.