I have sailed both
I was in the same position as you a couple of years ago, and chose the Capri 18 over the Precision. But it wasn't really about sailing characteristics, but more a desire to really downsize.The Capri is the best sailing boat I've owned. I sail in all kinds of weather (on a lake, though, so waves are never an issue - less than 3 ft. - but very choppy), and have never felt out of control. It is very stiff, points pretty good (within about 3-5 degrees of the fin keel Capri 22), max heel is about 25 degrees before weather helm starts getting too bad, but if you reef the main, it flattens out and takes off.We have 5 on our lake, some of them second boats for hardcore racer types, and I have never heard anyone say anything bad about how they sail.Having said that, I really like the Precision also. The P21 is a good bit larger, and from my limited experience a little more tender initially, but then similar.You might ask this question over on the Trailer Sailor site - there are lots of both Capri and Precision fanatics over there, and you will get plenty of feedback (all very objective, of course)