I like the Pfalz DIII, and the SE5a. The SE is just such a nice airplane and its long time of service is impressive. Plus it has the speed even late in the war to run away. The combo of a vickers and a lewis gun is fun for some reason. Not an overly glamorous ride and not a beauty like I think the Albatross and both triplanes are, but a good solid friend for a pilot.
The Pfalz also is just a nice plane to fly and I've done pretty well in it. Kind of has an identity to go with it being largely a Bavarian machine.
The Nieuports are also fun. They are just so great for when you want to dance around the sky and really mix it up!
The triplanes are exciting as well. Using they;re phenomenal climb i seem to get a lot of shots diving directly down on my opponents where I have a perfect top down profile view and shot- that's a lot of target to shoot at.
I haven't even go into flying a lot of the planes I've downloaded yet, so I'm not sure my preferences will remain the same. But I'm really enjoying these WW1 kites. I'm looking forward to giving some of the pushers a go too. Just so many fascinating aeroplanes and so little time!