personally I never liked Trilogy... the MK series really build as it moved along, adding new types of features it wasn't just new characters and arenas the game play changed with each version.
Trilogy didn't work very well because all the old characters were either worthless or too cheap against the more recent ones because they were meant for different gameplay environments and it just made the game incredibly unbalanced IMO.
UMK3 FTW it's only missing a small number of people compared to trilogy, it the fastest MK game, with the widest variety of finishing moves and probably the smoothest playing MK game too.
SF is great and all but I can't stand Capcom's combo system and the jazz music + childish anime style sprites were never that attractive to me either. SNK does a lot better with more of an adult anime style and more techno oriented music but the combo system is still too close to that of Capcoms. UMK3 was easily the best 2D version of the MK series, the best finishers, the best special movies and finally an actual combo system of their own. The combos were all essentially multi-part special movies but I still liked them more then Street Fighters, Graphics and Sound were a whole world better too IMO, not to mention they explored the arena's more with things like the various Pits or changing locations mid battle.
Nothing beats Killer Instinct IMO though, hands down the best combo system ever implemented in any fighting game EVER. It was open ended so you could make up your own combos but it was regimented enough that you could literally come up with a combo on a piece of paper try it in the game and it would work. Couple that with the most unique round handling system, finishers and exploratory arenas like MK but you have to perform them while you're opponent is still alive as well as great graphics and sound... Damn now I want to go play it.