Jeez, what a request - a single plane with no context.
So many I have not flown like the pup, DVII, DR1.
And I've not flown much in the early or late years, seems I tend to stick in the 1916/1917 years.
Only recently getting into 1918.
I've started a French Pilot a while back and got him up the the Spad XIII
When I first started WOFF, the N11 was not fun, a second go around a year later and it was a different story.
However when I first started WOFF - I recall graduating from the Strutter to the Tripehound was like turning on a light.
It was my first long lived pilot.
So while I really do not stick with a particular plane, I will have to say the Sopwith Triplane.
Even though I have yet to have another Tripehound pilot.