That all depends on how often you want to use it. It is very nice to have it ready to go if you do not want to mess around with the trailer or haul it back and forth. I know that Washington's landing has some in water PWC lifts, if any are available. I think that Peggy's does something like that with a small crane but not sure. I know that Newport has a few lifts but not sure on availability depending on how they did over the winter. Also some place like Lock Wall in the strip I believe allow for on-trailer storage with a ramp readily accessible. So you could use your own trailer and launch right there anytime you'd like, if they still have that service.
Depending on how secure the marina is, i highly recommend it, just for availability. Its a pain to launch a trailer every time you want to ride. If its on a lift or dock, you can just go.
Peggy's has about a dozen or so, and even has one for sale, brand new, if you need one.
SO, I ended up going with newport. The folks there were pretty nice and the price was right. Peggy's was kind of shocked that I was asking without also docking a boat - the answer was no, washingtons landing was 600 bux, millvale was 550.