I painted up two squadrons of killa kans about three weeks ago. I've played a few games of 6th Edition, the units that have scored the 'win' for me have been my boyz. With infantry able to score primary and secondary objectives, they are a must have. To support my boyz mobs I wanted killa kans with grotzookas. Their size, fire power and mobility are choice for their intended purpose.
I haven't made the grotzookas yet. I was thinking about making them, and then sending the final pieces to Anvil Industries for resin casting. Right now my killa kans have rokkits launchas.