Keeping it simple:
Ewers don't affect BLM or DRK (their relevant 'stances' disable all MP regen). Generally, if I see someone under 30-40% MP and I pull an Ewer, I'll toss it to 'em (BRDs included).
Spire is same thing: 30-40% TP, toss it their way. If everyone needs it, just pick one, or happen to have Expanded Royal Road.
Arrow is a straight up speed buff. Everyone can benefit from it, casters, ranged, melee, tanks, and healers. It reduces GCD for weapon classes, and cast time for casters.
Spear is a straight up crit buff. Everyone can benefit from it, casters, ranged, melee, tanks (to a lesser extent), and healers.
Bole is very situational, as you noted. Typically tank only if needed, and Royal Road/Shuffle fodder.
Balance is the one everyone begs for. Everyone wants it. Can't go wrong with this one. Slap it on a DPS of any kind.

For random groups, alternating who gets buffs is fine. If you forget your order, nobody really is gonna notice and it's not that big a deal. Even if you exclusively give buffs to one person, it's not likely to be an issue (in my experience anyway). Do note, some players will claim they don't want such and such buff for reasons (Arrow...). In statics, fine, coordinate. In randoms, you don't know if they care, I'd go with defaulting to they don't.