In my opinion, Sega, Konami and Capcom did the best beat em ups in the 16-bit era. With this genre being my favorite, some of the top ones that often comes to mind is Streets of Rage series and Teenage Mutant Ninja Turtles (both Sega and SNES).
Without going too much into detail in regards each game in the series as a whole, Streets of Rage 3 was the final installment in the series for the Sega Genesis. The sprite work was a minimum improvement (if any at all) from the second…not like the vast difference you see when comparing the original to SoR 2. The North American version that is shown in this post, the difficulty level is a lot harder than its predecessors and region counterparts.
Here are the images: