Say you are playing a song which is in E flat. I'll take Malmsteen's 'Rising Force' as an example. We play this song with our band. But the first time we rehearsed this our guitarplayer played it in E. He hates downtuning guitars. (his 'problem'

But the question goes for a LOT of songs where the guitars are downtuned in general. What do you keyboard players out there do. You stick with E flat (because that's what you hear) or do you transpose your keys? I actually dislike the use of the transpose-button but I have to admit that (for me) some parts are easier to play in E than in E flat...
I'm curious about your views...