Some interesting replies so far.
I usually gravitate towards schemes that contain personal markings of hearts, comets, and skulls.

Ones that are not frequently modelled I also find more attractive. I used to like the Fokker D-VII in the "Sieben Swabians" markings, but after Eduard released the special edition and you started to see that scheme modelled frequently, that kind of put me off of it then.
I can still remember in the mid 1960's when I first saw Revell's re-issues of their 1/28 scale SPAD XIII, Fokker DR-I & Sopwith Camel in the markings for Frank Luke, Werner Voss and William Barker and thinking who are there aces that I've haven't heard of before. Right away that made me want to build all three!

Also for german aircraft, ones that have odd early versions of the balkenkreuz markings that look like early WW2 luftwaffe crosses before they settled into the common narrow late war design.
Chuck