What works well for counter top?

[smatthew]

I prefer spar varnish to polyurethane. It's elastic, unlike polyurethane, so it handles changes in temperature and humidity much better than polyurethane.

In my last house I build an Island in my kitchen and for a countertop I used hardwood plywood and 4 coats of spar varnish. Lived there for 7 years and never had to re-coat it, and it stood up to being scrubbed at with no problems.

[WA]

I painted over 57 year-old formica with RustOleum counter top paint and it turned out quite nicely. I've seen the same paint used on MDF, so, don't know why it wouldn't give you a nice surface on plywood.
Best,
WA