Just noticed on here, that you can use 3 tin ore instead of 3 iron for the bucket.....
EDIT: The extractor takes refined iron for the machine block, not just regular iron
Noticed that too, and was doing it that way at first, but I noticed I seem to be more short on tin than iron usually.
I guess which is better depends what other mods you use as well. Forestry mod uses a lot of bronze.
If you use Equivilant Exchange then definitly make it out of iron (since you can't transmute copper and tin)