As a Dark Angels player I can't talk much about the Space Marine option. The basic differences between the armies is that deathwing terminators are fearless, they only get the old storm shields, they can mix and match (you can mix shooting and combat terminators in one squad) and you can only have units of 5 terminators.
The Ravenwing and Deathwing always work well together as up to half of your terminator squads can make a deathwing assault, (deep strike on the first turn without having to roll for reserves) while the bikes come with a teleport homer and the scout special rule. So deploy the bikes 12 inches on, move 12 with the scout move then turbo boost and deep strike the terminators near the bikesso you don't have to roll to scatter. This lets you get right into the enemy or into a key position early on.
Also, if you take Sammael you can make bike squadrons count as troops, while if you take Belial you can make terminator squads count as troops. I've found that a fearless terminator squad with storm bolters and an assault cannon sitting on a objective is a difficult obstacle to remove and can dish out it's share of damage while it's there. Also Belial and Sammael let you upgrade 1 terminator and 1 biker respectively to a company standard bearer, giving everyone in the unit +1 attack and allowing morale re-rolls for all units within 12 inches. If you tool up a combat terminator unit and rush it into a unit holding an objective, not only can the terminators kill whatever's holding it, but they can secure the objective as well.
The bikes can also do their bit too, with twin linked bolters that can fire on the move they're a threat to infantry, and their fast movement makes them an ideal objective-grabbing unit. Be careful in combat though, as there they're just toughness 5 marines.
If you take a pure Ravenwing/Deathwing army, you get a lot of flexibility when deploying due to the bikes' movement and the terminators' deep strike, though units could easily get isolated and quickly get swamped if you make a mistake. Also due to its hight points cost, you'll end up with an elite army with few models, so the loss of a even a few models can be a serious setback. (and therefore develop a healthy fear of plasma cannons). The army also has no ranged weaponry with over 24 inches range, so any long range support units the enemy sets up can really be a problem.
Hope this helps.
"I roll and run forward 2 MIGHTY inches!!!!!"