vague answers to a vage question..
if i am farming legendary/fabled my bruiser does the job better than any other, because i can flop through a zone quickly and easily just killing the named.
if i want the XP along with loot i would play my zerk, if i wanted something a little in between i would probably roll a SK. pally i would say is probably very similar to zerk in many respects in heroic areas. SK has the zerk beat in soloability and ability to rank on tons of mobs while healing himself with their health, moreso than zerk.
one SK a**hat trained me so i decided to return the favor, he took every mob i could find and turned them into batteries, i felt a little disgusted because these weren't exactly green single ups but blue ^^^ heroics and he had about 20 or so on him when i dragged as many as i could find on him. there was no gear that i could have had that would match what he was doing, so.. was one of the best outfitted zerks on the server at the time, i could do close but not that well.
zerk = lazy easy AE and xp. round up mobs, click attack and watch TV. SK takes a little more work but does it better. never played a pally.
i won't bother comparing the guard, probably the slowest out of the bunch with little solo utility.
so, ultimately the answer of a leather tank class is true. though they do not have a very strong AE ability like SK/zerk/pally, pally being just above the leather fighters. SK/zerk are best for boxing toons and power levelling little ones or in AE focused zones that you don't want to bypass mobs in.