So far, for the books I'm interested in, they're about the same. It's always good to have more sources, but the prices seem remarkably consistent (within a dollar or two for small things and 5% for bigger ones). Part of this is I'm looking for books that I think are only sold by certain vendors, which is probably at the root of the problem. It's probably the same people just selling through different front-ends.

Thanks for the rec though.