http://raidcomp.mmo-champion.com/

Buffs don't stack as a rule of thumb. MOTW will not stack with MOTW, nor will it stack with Blessing of Kings.

A lot of people build groups based on buffs. They're looking for maximum synergy among their group. For example, I consider throwing a Feral druid in to my group to replace my husband's DK {in sig}. I'd gain Critical Strike Chance from LotP, Stat modifier from MotW, Armor debuff from FF and +bleed damage from Mangle.

BUT - I already have two paladins, one of them is always providing stat buffs from BOK, none of my other guys use bleed damage. That makes it less "useful" than say using a Fury Warrior, which gives me both the crit strike buff and the armor debuff, as well as a healing debuff. Or perhaps a hunter where I can use pets on a case-by-case basis to provide whatever might be most useful at any given time.