[quote=@Jbcool]- Imperial Guard, something like a mix between Band of Brothers and Gaunt's Ghosts, a somewhat closer-to-real-life RP that I expect would be darker and grittier than the rest.[/quote]

In my opinion, the greatest strength of the [i]Warhammer 40,000[/i] universe is the juxtaposition between the extreme horror of the galaxy and the human spirit. I am a great fan of the [i]Eisenhorn[/i] and [i]Ravenor[/i] Inquisition novels for their storylines, characters and exposition on the galaxy and the lore, but the [i]Gaunt's Ghosts[/i] novels hold a special place in my heart for their depiction of the struggle of regular, ordinary humans to stay... well, human. 

So the quoted option above has my vote. Astartes are too easily made dull and I don't like the idea of commanding multiple units.