What year is the Cervelo? The previous generation of R-Series is definitely somewhere between a racing and endurance geometry. I would describe it as a very aggressive endurance bike. It's still light and stiff as a race bike should be. My experience is with an R5 but I'm 100% sure R2 is just as great but a couple hundreds heavier.
I have no experience with Giant and I'm sure it's a great bike but I have nothing but good things to say about a Cervelo R series bike.