Finnish US Brewster (F2A1) BW-364 is credited with 42 1/2 kills by all the different pilots who flew it.
This quote from Wiki: After evaluation of claims against Soviet actual losses, aircraft No. BW-364 was credited with 42½ kills in total by all pilots operating it, possibly making it the highest-scoring fighter airframe in the history of air warfare.
Another source credits BW-393 with 41 kills. If anybody is good at counting, this site has a list:
http://www.warbirdforum.com/scores.htm
Always like that the main pilot that flew this aircraft... His kill markings were beer bottle labels