I have DRG, BRD and MNK at 50 and DRG and BRD seem to be most fun thus the easiest for me. MNK just have too much running around the target and his skills are set so that you don't have much room for improvisation when something goes wrong - at least it is much easier for me to change and adapt to situation with DRG or BRD. Haven't leveled mages much because I don't like the concept how their jobs work but it does apply to almost every single game I play that I avoid caster jobs.

DRG - most fun and most versatile
BRD - most safe because you can walk around where you want all the time
MNK - most awkward and kind of boring
casters - don't use/no idea