I think CP3 and BRoy have very similar value in the league. I may be a homer for saying this, but I'd pick Brandon over Chris because he's bigger, all things being otherwise equal (or at least equivalent)...
I'm glad you mentioned Rondo and Allen that was a glaring omission. Still I think you have to consider Portland's back court right up there with any in the league. There isn't one out there that leaps to mind immediately as vastly better. Obviously Rose and Gordon would be in the mix if that pair had been kept together.
Well according to ass clown.... er Mr. Sonic, our back court will be Blake and Roy. Roy is a top 5 starter in the league, and Blake is a bottom 5 starter in the league. That puts us average at best.
Ray Allen's production is about to fall off a cliff. He is getting very up there in years for a SG. But of course you could count Paul Pierce as the SG then, and then Boston really would have the #1 backcourt.