Perk is the most efficient player of the group, but I agree that there's a huge difference between "best offensive player" and "most efficient player". Also, you need to look at assists, offensive rebounds, and turnovers when assessing offense.
It's interesting that Perk actually generates more unassisted offense than, say, Krstic does. I think Perk's offense was underrated, as he's made some real strides there. However, Krstic and Murphy stretch the floor and open up space for Rondo, so that's a benefit.
In terms of overall offense, I'd rank the guys Murphy, Krstic, Perk, BBD. Defensively, it's Perk, BBD, Krstic, Murphy. (Sorry, BBD fans. He's more versatile than Perk on offense, but I think Perk is better on that end.)