varnish

[LeeG]

is there any reason to use polyurethane varnish over regular varnish or vice versa?

[JimD]

The polyurethanes usually are offered completely clear if you don't want to amber tint the wood whereas a traditional varnish can't be clear due to the organic ingredients. Two part poly's are the hardest topcoats available. Polyurethanes will cure faster as well.

[Bob Smalser]

...and the other side of the coin is they can be a bit more brittle and have a plastic look and feel some dislike.