let's say the #1 and #2 guy in the division or simply just the best fighting the best... a highly ranked guy vs another highly ranked.. examples: Rigo Vs. Donaire, Canelo Vs. Trout, Garcia Vs. Matthysse, etc or a Guaranteed FOTY candidate with two action packed fighters, that are decent, but not considered to be great.. examples: Rios Vs. Alvarado, Froch Vs. Kessler, Lopez Vs. Maidana, etc :think
Froch Kessler was the best fighting the best. It doesn't necessarily have to be #1 and #2 if its high ranked fighters fighting each other then that's the best fighting the best.
to be fair tho, Garcia-Matthysse kind of qualifies for both sections.. this is the best against the best AND could end up being FOTY
neither is #1, each had 2 L's on their resume, and they aren't prime.. guaranteed excitement, but it's not like this was a career defining fight..
This doesn't exactly address your question, but in terms of style matchups, I really enjoy a boxer puncher vs. a brawler. There is always the drama of will the boxer puncher be able to outclass the brawler, before the brawler can land his power shots ie Mayweather vs. Hatton or Matthysse vs. Peterson.
Neither Ward nor Gatti was the elite of their division when they fought, but man was their fights awesome!
Barrera-Morales, Chavez-Taylor, Vazquez-Marquez, Leonard-Hearns, Marquez-Pacquiao... Ultimate examples of EXCITING FOTY match ups that feature the best of their divisions.