[Taqwus]

If you've done the research, and have both the death-7 and nature-4 (GoR) casters, it's hard to beat Tartarians for their sheer hp and other base stats, their frequently useful innate magic (and the earth/air guys are fixed), full set of slots (for the humanoids), zero enc... they're not ethereal, immortal or flying (other than the Manticore Monstrum) but they're very, very buff.

Among uniques, Ambicephalos the Ettin Mandragora deserves a nod for good base hp, decent stats, three hand and two head slots, sleep vines, and recuperation.