My favorite? My namesake - Kaiser Tarantula, my often-crab-spider sometimes-a-bane arachnos soldier. Had enough guns hidden on him to start a war or two, and punched out Lord Recluse in the the World's Greatest Spider-Off in several different near-future apocalypse timelines, multiple times (I loved helping people with their villain patron arcs).
ARACHNOBOTS, ATTACK!!
Ahh, fond memories.
My favorite NPC? Probably John Temblor, aka Faultline II. Sure he was a cheatery bastage that combined stone armor, stone melee and earth control all on one character, but I liked the fact that he shaped up nicely after the Faultline arc, and in the RWZ he was easily the most capable ally you could have (sorry Sefu Tendaji, I have a lot of love for you, but Faultline generally kicks more extraterrestrial rump.)
A close second would be Black Scorpion - simply because, in appearance and powers, he's kinda what I originally envisioned Kaiser Tarantula to be - a brutal, heavily-armed high-tech killing machine with a man inside it.