I used to play MHF2 and MHFU on xlink-kai a lot. It's really good, but it has some flaws. Also, it's not compatible with all dongles. Furthermore, some games are a pain in the ass to set up(the 1st dissidia was). Adhoc Party is for sure better.
Pretty much, ever since I got a PS3 and adhoc party, I have no reason to come back to xlink-kai.