I'd start Pruitt at point, because a) Pruitt is so much better defensively than Marbury, b) he's been with the team longer and may (I emphasize may) know the plays better, c) he may (see last point) be a better outside shooter than Marbury at this point, and d) I think/hope that in the playoffs Marbury will continue to be playing mainly with the 2nd unit players, and I'd like to see him continue to develop chemistry with them. House was completely neutralized by playing PG against Orlando...he made a big 3, then the next 5-6 times up the floor he brought the ball up the floor, passed it off, and never got it back. He's just so much better playing off the ball, with a PG like Marbury looking for him.
The PF position is a tough call...the Perk/Powe combo is so good defensively at cutting off the paint (important when playing with Wade and JO), and I like Powe matched up against Haslem, at least compared to a 3pt shooter like Beasley. But who plays for Miami's 2nd unit, who would he match up with? Powe against Joel Anthony is fine with me, and have Pierce and/or Walker cover Beasley. So I'm not sure there's a clear advantage to Powe or Moore here.