Nobody has more powerful versions. All raid buffs are identical in power in Cataclysm. Some have different durations or radii or other measurements of convenience. “I won’t get brought because his buff is more powerful than mine,” is a pretty reasonable argument. “I won’t get brought because his buff is more convenient than mine,” just doesn’t carry the same punch.

Players are going to find themselves in situations all the time where they bring the same buff that someone else brings. Shaman and paladins are probably in the best situation of bring able to bring something no matter what else the group already has. But we still want for groups to be able to bring say two Fire mages, and in that case, their contributions are identical. (Source)