its Ghazghull no ifs ands or butts, he started his career by being shot in the head by a bolter (
IIRC) and after "repairs" he started hearing the will of Gork and mork, beat, killed and bullied any orcs in his path to follow him and waged a sector wide assault on the
IOM, all this from spore...
Most of the others on the list are super-enhanced thingma-bobs or GODS, or splinters of gods etc, But Ghazy has style, and drive, and nobody tells him what to do, except maybe Gork and mork, and Ghaz has the stones to tell them to zog off if he wanted too!
And on a side note, in a mega game I played against a awesome orc player that had Ghazghull leading his forces, and during the game a Reaver titan stepped on old thrakka who used his invul save to survive it,and then attacked the titan in the following round and inflicted 3-4 structure points to it causing a chain-reaction that crippled it, ( we imagined Ghazghull hanging from its foot ripping stuff outta it and cursing at it all the way ), this was followed with cheers from everyone at the table (except for the Titan's owner who got all butthurt), now that is man..er Ork.
Also Yarrick lives because Ghazzy let him, ole thrakka respects his foes and likes to keep the best around to keep his life interesting