I feel that the Space Marines are going to be over-populated by the community, and besides I equally enjoy both contrasting factions, yet I have much more interest within the Chaos. Plus, I like the idea of moping around the gamescape doing vile shit an necessary endeavor to be cleavered onto another Astartes beaver, for they're believers of an ominous deceiver that which consumes their mortal weavers.
Orkz because well they are tons of fun on the table and I love tormenting my friends with them. Nothing better than meganobz and a warphead in a battlewagon right...
Space Marines. As long as the Space Wolves are still loyal to the Emperor then there is no way the Imperium could fall, just ask Bjorn.