Your favorite model/unit
I can't believe this kind of thread hasn't appeared yet but what is your favorite model/unit? This can be for any reason be it tactical, painting potential, fluff, etc.
Grey Hunters Pack w/ Wolf Guard - All in a rhino with MotW, meltagun, standard, combi-melta, and power fist. This squad is my go-to jack of all trades and they never let me down.
Bjorn - Invincible dread with a plasma cannon that hardly ever misses? YES PLEASE! Plus the fluff for him is really cool.
Kharn - One of the best heroes for his point cost. If only he had eternal warrior or T5 he would top my list.
I technically have a lot of "favorites" but these are some that immediately come to mind.