Ubuntu on the desktop - flash plugins

Hi all,

I'm working on migrating users to Ubuntu as their desktop, one of the little gotchas I have is not knowing which is the best flash plugin to use with firefox.

Adobe have abandoned flash on Linux as far as I can see and I'm currently using gnash but users are being prompted to upgrade their flash players when visiting YouTube.

Would anyone have any suggestions on the best option for flash support?

edit: chrom(ium) is not an option, policy is for Firefox.