D'Addario phosphor bronze mediums (.013 high E) on my Guild, Palmer and Cort -- the Palmer being tuned pretty consistantly to open D and the others in standard or drop D.

I was a bit surprised to find my National Steel came from the factory with the same strings. Not sure they're D'Addarios, but they're definitely P/B .013s and they sound great, so I'll stick with them. I keep it tuned to open G or open D almost all the time.

cheers

david