Here's a hypothetical. If it would cost the same amount of money, who would you rather have as the back-up point guard: Marbury or Pruitt? That's a big if, of course, and there are other options out there, but I think the answer should be Marbury in that forced choice.
What it comes down to is this: I suspect that it's Marbury or nothing. If the Celtics sign Marbury, then the backup backcourt will be Marbury and House. If not, it will be House and Tony Allen. Both have flaws, but which one do you think is more flawed?