Here, I’d like to break down the strengths and weaknesses of the two aircraft. Here's What You Need To Remember: The biggest difference, perhaps, is in numbers; many hundreds of F-15s continue to serve around the world, while there are fewer than a hundred Su-35s. I have been asked to compare the venerable American F-15 Eagle fighter to Russia’s new competitor for the crown of best Fourth Generation fighter, the Su-35S “Flanker E.” The former is the airplane that in many ways defined what a Fourth Generation fighter can do. Introduced in the 1970s, it has been extensively updated to keep with the times—and hundreds will remain in service for decades to come.