Not explicitly, but I think I generally tended towards giving Cloud Lightning, Tifa Ice and Red XIII Fire. Other characters I never really assigned a preference.
Before I started making a character into a designated magic user I tended to favor Cloud with the 'cooler' spells, Bio, Demi, Comet.

(Ironically from the thread title, if we were going with real world elementary forces then Gravity is the only one on the list that makes the cut. )