Maybe Knights and Trading Post would be better buys, but generally, I do like Rebuild first. But I'm often wondering about the second Rebuild before the first Duchy, though.
You want the second Rebuild before the first Duchy. The first Duchy doesn't do anything, but the second Rebuild quite potentially gives you at least one Duchy before the Duchy pile runs out.
...which is exactly the Duchy you could have bought for $5 instead of the second Rebuild.
Yeah, so if you gain exactly that one Duchy, it doesn't matter which one you bought split-wise. But now, you just have a Rebuild instead of an Estate in your deck.
It depends on the situation though, sometimes I feel like I don't have enough time to use the Rebuild before the Duchies are gone, and I'll buy the Duchy in that situation even if I only have one in my deck.