Former day sailor owner
You have some apples and oranges in your mix of choices. If you don't mind getting wet, then of course get a Cat and be at one with the water, so to speak. If you want a nice afternoon's sail, with cooler and gear on board, then get a day sailor. However, you must manage your affairs so that you never, never capsize it. If you do, there goes your cooler, perhaps other gear as well, and you won't be able to get it back up again.I owned my boat four years and never capsized it. If I bought another one, I would get a storm jib and a reef points added to my mainsail, because I generally had to drop sails and motor whenever the winds approached 20 mph. I had a wife and small child on board, and capsizing just wasn't a risk I would take.That brings up another advantage of the day sailor over the Cat. You can put a small outboard motor on the day sailor, and give yourself a lot more maneuvering room in marinas. You also give yourself a way to get in quickly on a calm day, or in advance of approaching weather.I didn't try to put a porta potty under the small cuddy on the daysailor, but it would have been nice to have one. That's where going a little bigger, to the pocket 21 or 22' cruiser, makes some sense. You have a place for a potty, and you have a keel (or water ballast, in some cases) for extra stability.As for the Lightning, it is a higher performance boat than the day sailor, has no storage cuddy, and for my money would be preferable over the day sailor only if you wanted to race it in class races at your marina.