I-153 gets my vote. I love that airplane, and it is also considered to be the best biplane to be built, however I also think that Gloster Gladiator is also a very reliable and agile biplane fighter.
To sum it up, these two are my personal favorites.
There were some Beech Staggerwings used in the PI. Can't remember the AAF designation. They were not used as fighters but wonder how they would stack up against other bi planes?
I found my reference which had Staggerwings in it. The RN used them and called them Traveller I. The AAF called them YC43s or UC 43s. They had a V max of 195 mph at 5000 feet.