+1 to 1007. That is a great strain, and it's clean enough to use in other styles as well. But honestly, I'm a believer in 1007 for alt, 2565 for kolsch. I know the yeast makers sometimes list these types of yeast as substitutes for each other, but I don't get it. Kolsch yeast has that vinous, distinctive character - if it were used in an alt-type recipe it would seem like a 'malty amber kolsch' to me. On the other hand, you could use 1007 in a kolsch and it would be very clean and have no kolsch yeast character. Not saying either beer wouldn't be good, just not the real deal.
EDIT - OTOH I'm not always a style nazi, and I've made a lot of good beers that didn't fit any set of guidelines.