Sega Master System / Mark III / Game Gear
8-Bit beat-em-ups have always been a mixed 'bag'. Everyone screams for Street Fighter 2, and we've had a fairly decent version of Mortal Kombat 2, but if you prefer the cartoony style of SF2, then you should be more than happy with Fatal Fury.
Surprisingly, all the characters and backdrops have been included, but obviously some of the moves have had to be sacrificed - just two buttons, y'see. Con a 'chum' into parting with cash for another copy and you can have a two-player link-up. Tip toppity top. And until the day that SF2 does come to the Game Gear - please don't hold your breath (you'll die) - this is a darn fine alternative.