Well it depends on what you're doing (as always) :P
I like /rdm sub for general use, gravity in my book is just, amazing. It's also got it's fast cast, access to enfeebles you otherwise wouldn't have (para, slow, etc), it's average for healing ability, get regen and cure I-III (atm), uh, refresh is a +.
/sch has some SERIOUS usage now. For example, low manning dynamis or w/e where large crowd control is required, being able to AoE sleep, bind, break, stun etc is well, awesome. Elemental Celerity and all the little nice boosts the stratagems provide.
/whm has it's usage if you feel you need a little more bang in your cures, giving you access to Cure I-IV. Reraise is a huge plus. Auto regen, in my opinion is extremely irritating(i use sorc.), although every little helps i guess. Divine seal for serious bang in your cures.
/nin is also just as good for maybe solo/duo with ***that likes AM/Tier IV+ or even just as a pose to any of the others.
It honestly just depends on what you want to use it for.
My advice, not that you care, is to level them all to 50 at least, and play around, ya never know, some might surprise you ^^)