Forumites: good topic with lotsa educated comments. Am glad to see that Dr. Frank will pitch in, because when it comes to air combat stats, he be da man.
Most successful? As noted, we require a definition of terms. I quarrel with some well-regarded European aviation writers who claim the MiG-21 is the most successful jet fighter just because so damn many were built. That's fine if you're from marketing: if you're in the cockpit looking back at your 5 to 7 o'clock and can't see the bogey, it ain't worth a damn. Personally, I abhor the concept that any fighter with a negative kill ratio is somehow "successful."
As for Albatri, consider MvR's 1918 comments: "a tired old bus" or somesuch. The type was kept in combat well beyond its prime but was available in numbers--despite well-known structural faults. Those who attend our CFM event in February will see the common field mod: an extrnal brace running from the V strut to the leading edge of the wing to reduce flutter and vibration. I suspect but cannot prove that the sesquiplane design of the Pfalz, while externally similar to the Albatros, was better constructed. That might be one reason that some well-regarded folks like Berthold preferred the Pfalz.
BTW: I have it on good authority that
Billy Bishop never flew a Pfalz, and MvR never shot down an Albatros. "Can we just get along?"