Assuming the following:
Right now, for painting, I'm considering the two models that did well at the GD last year: the Doomwheel and the Warlord.
I'm leery of doing the Doomwheel, though, because of
I could also do my War-Litter Warlord or even my Warlock Engineer (both below).
For conversion, I'm considering my Facebook pseudo-internet-famous Hellpit, my War Litter, my Warlock Engineer or maybe a Mortar.
Leaning strongly away from those last two: the mortar's just too rough, and while the Engineer is fantastic, it's barely converted. So, really: Hellpit or War Litter?