I would say Gunstar Heroes
Sonic 3
marvel vs capcom2
DC online
Awesomenauts
Gunstar Heroes because I love how fast and action packed it is. Also keep in mind it had an anime feel to the characters which was cool and not seen very often in games during the early 90's if you lived in the U.S
Sonic 3 because on a grading scale I feel it was the best sonic game of all time. you can use tails in sonic 2 but you can't fly with him sonic 3 fixes this. Knuckles was added to sonic 3 and part 2 which is sonic 3 and knuckles he is playable.
lets also not forget the birth of hyper sonic and the only game he is featured in. Gameplay is smooth thought there are some glitches but more forgivable for a 90's game then games in the current gens or for dream cast. Thats right I said it, the adventure series is over rated! I loved it as a kid replayed it as an adult and realized it was not that great and had more bugs than the genesis games. I mean how do you get better technology and still come out being worst.
Marvel vs capcom 2 to this day is still known as one of the best fighting games ever created. 3v3 high speed fights with over 60 playable characters. Megaman, ken roll, juggernaut Akuma. Marvel vs capcom 3 is not only slower paced but the line up is not nearly as memorable as the MVC 2 cast.
DC Online Literally woo'd me. I hate MMo's they are really slow paced games that are not innovated enough to be found interesting by me. This is where DC online is different, you get a lot of different powers, and weapons to have all types of intresting ways to beat enemies. Also DC online is fast paced, you can dodge attacks, combo people and interupt their movies. Most MMo's do not have this many options in combat. You can usually only dodge or mitigate dmg by proper party MP utilization and DC online breaks that mold. Last but not least awesomenauts. I do not care for MOBA's the community of people are rude and most of them are slow paced too making it feel like simply playing pvp in a MMO with a few added objectives to them. Thought the community is also rude Awesomenauts breaks this equation. Now I will admit the graphics are not as impressive as LOL or DOTA but it is a lot faster paced to where you can dodge attacks, counter and combo people. The developers also put a lot of love into their characters with cool taunt's catch phrases and their own custom songs when you select them at the waiting screen for the match to begin. I myself am a very competitive person and games with out speed do not feel competitive to me. For a game that cost $5 awesomenauts is a great pick up for real competitive gamers.