From Hunter and CL point of view.
Running with 2x SP, 2x Hunter (SV + BM) most of the time so:
1.
ranged: 2mages+elemental+bm hunter+SP
Contrary to belief all classes (can) gain 101 spellpower (read scorpid poison for hunter) in that group. While no one complains about +3% damage, and or mana/hp regain.
2.
For rest of classes i think arcane mages and ele.shamans benefit most from mana regain.
(don't have boomkins) difference really shows for those 2 as I noticed. On some fights (specific) healers are clearly top choice or AoE folks.
Hunter specific:
For Hunter mana alone I dare to say, MM hunter is currently biggest mana consumer then SV then BM. But BM is only spec that gives and takes to/from SP (damage for mana/hp) thus placing with SP.
MM and SV hunters doing max dps are using max special rotation that burns mana faster than anything but don't contribute to caster group dps sadly. Luckily BM is also great dps at the moment.
I'm SV speced and chain pot + dual mana oil (+mageblood) so i can handle most of longer fights with only manaspring/tide (while getting GoA also for 99agi to me = 25ap rest of raid) so I'm usually in healer/mt/leftover group. (3-4 shamans/raid here)
While this might mean I burn more consumables than most of people, i do have FD that saves those sometimes on a wipe
