On fun factor from my own perspective I'd have to vote LaTale.

Fiesta ~ Is Ok but a very generic MMORPG
DFO ~ Fun if you like brawlers or Action based side scrollers
Mabinogi ~ has a lot of stuff to do and can be very enjoyable, it's just the learning curve that can be a huge turn off.

If you don't have a lot patience and still want a fun MMORPG, I'd go with LaTale.