What I care about is having fun. When I aired this concern to the staffer at my local GW, I stated that I was unsure whether I would go with:
Mantis Warriors - Space Marines
Iron Warriors - Chaos Space Marines
Nurgle Chaos Space Marines with Chaos Daemon Allies
Word Bearer Chaos Space Marines with Chaos Daemon Allies
The staff members response was "Nurgle, mate! Their bikers are Toughness 6!" - I don't like the biker models or the idea, and he's assuming I'm one of those "play-to-win" types (which if you've seen my 40k Playstyle you'll know simply isn't the case - I go fluffy to the point of not viable!)
Even as I type this, I can feel the lure of Chaos away from my Mantis Warriors... It probably doesn't help that these arrived on my doorstep yesterday...
And now I'm trying to decide on a colour scheme for them.
If I did Word Bearers, which have always been my true Chaos love... the red and silver would look nice, but quite similar to the BFG studio fleet...
If I did Nurgle, the green and silver would certainly be unique.
If I did Iron Warriors, it'd be successive silver drybrushes and some yellow and black details on the prow. Certainly the simplest and most striking...