Space Marines FTW!
Space Marines are hard as nails, and they have far more clout polititally than Imperial Guard. Numbers can be swelled and Fluff Wise a Space Marine could easily take on 10 IG each without a scratch anyway. Not to mention Legions of Vehicles, Titans, and most likely the best part of the whole Inquisition (GK and Deathwatch would fight for SM as a minimum).
Numbers count for alot, but bear in mind the Imperial Guard is a MASSIVE organisation and totally spread out. A Chapter of Space Marines could take IG held worlds one at a time - th SM wouldn't have to face everyone at once.
Space Marines, i salute you
