It's a coin toss. The 906's are early heads that suffer from a small SSR that will give better low lift numbers but need work at the higher lifts. They're also kind of fat around the valve guides and the seats are soft. The 452's have hardened seats, better swirl but are a lighter weight casting so the crack potential is a little bit higher although one that is not common. The ports on both are supposed to be from the same molds but as with any casting process they suffer from some core shift. The 452's tend to have better intakes and the 906's better exhausts.
If I had the two in front of me I'd go with the 452's just because they're slightly less work to get good numbers from.