This is really a half and half topic. You could really
only like the spells or you can only like the character.
I gotta go with Strago. The silly old man with a mohawk
was a welcomed addition to the party and I always loved
his Blue magic attacks as most of them were actually
useful. Second on the list would have been the Enemy-
Skill materia as it has been a life saver in almost
every playthrough of that game.
I never used Quistis, Quina's spells ranged from useful
to why the smurf the smurf do I have this spell plus Quina
would get really smurfing annoying most of the time.
Kimahri.... HAHAHAHA yeah smurf Kimahri. FFV was not a
really fun title and I couldn't appreciate the Blue Mage
Job in it.