It's funny how personal preference comes into play with this stuff. I've never had a kayfun leak, and find it much easier to refill than a carto tank. I don't mind sucking out the juice with a syringe if I wanna rebuild or rewick, just takes a sec, and I'd much rather deal with that than a ceramic, nr/r wire, etc. Now, that being said, I'm actually considering a sophia or diver to get some of my pretty tanks back in the lineup.
KF's setup properly don't leak unless you change pressure. My daily change in altitude during my commute is enough to make KF's leak. Also, if you hold it in the wrong position in your hand while you walk, the swinging motion of your hand can make it leak.
With that said. I have 4 KF's, Russian, Taifun, 2 divers, 5 Sophia's, 5 different Gennys and over a dozen other tank type atty's. I've used them all. Side by side. I use 5 different attys almost every other day.
You're right it does come down to personal preference. I was only lending my preference after experiencing them all.