The next thing to compare is the riders themselves. The bikes & riders are pretty much the same. They both have hit & run, combat squads, and They shall know no fear!. So now the differences. White Scars get +1 strength to their hammer of wrath attacks. Admittedly cool. And they automatically pass dangerous terrain tests. Useful, but you need to fail the test and an armor save. Not really that likely to fail anyway. Their maximum squad is 8 bikers and an attack bike. Now, Ravenwing. They only get grim resolve, which is better, in my opinion, because it is coupled with hit & run. By itself, grim resolve is better or worse depending on the situation. Ravenwing squad is 6 bikers, an attack bike and a land speeder. I love that land speeder in my units because it is separated off from the bike squad. You could possibly have 4 scoring units from 1 choice. That is a great bonus in objective missions.
After that is gear. White Scars can take the grav guns in their squads. Ok, slight rant here! Why is that every space marine chapter in the galaxy has figure out this grav gun technology except for Dark Angels, Blood Angels and Space Wolves. I still feel bad for the Space Wolves. They haven't figured out how to fly yet. And why haven't Chaos marines figured out how to put a heavy weapon on a rhino! Ugghh! It just grates me! Ok. With that aside, the Scars get grav guns. Awesome! Ravenwing have the only imperial jet bike, the dark shroud (which confers stealth within 6"), black talons (twin linked plasma guns), and the Dark Angels standards.
So, in my honest opinion, it really depends on what you want from your bike army. If you want to smash into the face of your enemies, the White Scars are for you. If you want to shoot the enemy and avoid damage, The Ravenwing is for you. The best thing about this really is the fact that you could ally them together and get everything you want. So, have fun and ride hard!