I suggest Mermaid Dungeon PQ until 95 or whatever you want to do and then do the Ghost Blue Key Quests. They're fairly easy if I recall correctly and if you want Base Exp fast, it's the best way to go imo.
Most people powerlevel these days, not many grinding parties anymore. I only powerlevel because I put in the effort to powerlevel myself, rather than paying money for someone else to do it. It makes me feel marginally better ha.
Sadly you won't see any grinding parties anymore. Bugbears is gone, SF3 is gone, Tech4 is gone, and Tap1 is gone. Swamp 6 iirc is the field there people trained often, and that is also gone.
(Gone meaning no one trains there anymore, of course)