When I first read this thread I was going to write "Deffkoptas, hands down" but after reading the posts here I´m definately trying out warbikers!
With that said, I like what the Deffkoptas do for my army. They create a distraction that my opponent has to deal with, which results in fewer shots going into my boyz, and can take out tanks real quick to boot! They ensure that I have constant pressure on my opponent from turn 1. First the Deffkoptas go in, then comes the Trukks and Battlewagons, and last the big throng of boyz sloggin it across the field. It has worked for me every time.
Deffkoptas, Warbikers and Snikrot-led Kommandos are all good against
IG, so go with what you like the most