Found this on the internet. Sure, the first page and most of the second are respectable, but the further down you go, the more ridiculous it gets. there are SLCs, Boomerangs, Toboggans, and several kiddie coasters towards the bottom.
http://roller-coasters.findthebest.com/
Goliath and Mind Bender at SFOG may be well liked, but I feel they deserve even better.
As for actually underrated coasters:
GASM at SFOG is an old school airtime machine, but no one ever says so.
Hurler at Carowinds still brings the even with the trims.