Too bad Grey Knights aren't playable, but would be very hard lorewise.... Ah well, there are hundreds of other Chapters amongst the Space Marines. Bet there will come plenty more to chose from!
Honestly it's hard to choose between the Dark Angels and Space Wolves, but I think the Dark Angels have much better lore behind them.
ULTRAMARINES! The ONLY place where you not only have COURAGE but also HONOUR! And the most beautiful planet - Macragge
I loved the Dark Angels and the Blood Angels but I must vote for the Ultramarines because after I read the recent books and lore on their primarch I found the legion I thought mostly as very lame are actually my new favorite. Their approach to the universe and to the people they protect embody everything it means to be a man and a post human. I can not even understand why people like the wolves. They are a disquieting aberration of the emperors angels. I am happy to find out in recent books that the inquisition is actively hunting the space wolves. They murdered the Thousand Sons and there constant acts of barbarism are hardly fitting of a space marine.
The Wolves act the way they do because they couldn't be very chummy with any other legion pre-Heresy or post-Heresy either they were meant to be the Legion that could do what was necessary i.e. fight their fellow Legions if it came to that the reluctant executioners if the Emperor called them to this task. Also they may act arrogant but they are very compassionate towards reg humans look at what happened after the First War of Armageddon the Wolves fought the Inquisition tooth and claw to save the surviving human defenders from death and inhabitants from sterilization and eventual death in their work camps for merely seeing a demon or Grey Knight.