Well, I enjoy orks because they are unreliable and have a tendancy to do the unexpected and are just plain fun.
Space wolves are effectively Space Vikings and considering that is a topic I am rather interested in and have researched quite a bit they speak to me as well.
My other army is the Raven Guard. I have always been a fan of stealth tactics and the fact that they fight for the people, rather than the symbol of the imperium, there have been one or two occurences where the 3rd (under Shrike) have refused to join other imperial armies on worlds where battle rages hardest, instead preferring to fight on planest already abandoned by the main imperial army to save and protect the still loyal citizens on them. Shrike is to orks what snikkrot is to imperial guardsmen (their worst nightmare)