I'm bored with the repair sections lately, glad I found this place. lol, this is a very interesting age-old discussion.
speaking as someone whose family operated arcades in the 70s, 80s and 90s, they were always on the cusp of all the latest and greatest shit. they passed on SF2:TWW, cause who knew that game was going to go over as well as it did? when Champion Edition kits started flying out, we were there right as it was released. ours was in a Dynamo Z and well... magical things happened that summer.
after the summer ended, and I'd finished beating the game with every character (that was my goal in '92) that was it for SF2... then spring '93 rolled around and we got this game called NBA Jam, and after school one day I saw the rest of the room filled with Mortal Kombat and Time Killers.
I initially was reluctant to even touch MK. had nothing to do with the blood, it was just I felt like my allegiance was to Street Fighter. then I played it, and my life was changed. in the short term, back between 1993-1994, Mortal Kombat received the nod over Street Fighter in my book. the violence and shit, that was edgy, and it was cool.
then I discovered Killer Instinct in 1995, and I didn't care about either game anymore. KI had a unique perspective on how to do fighting games, and we joke about the Japanese/American thing like it's a joke for Americans to do a fighting game, but these were Brits doing this one! the whole combo theory thing, I thought that was awesome. I get absolute pure joy from playing that game now that I have dedicated KI and KI2 machines... the whole muscle memory thing of executing combos, that's so badass to me.
but go back to 2000, that's when I discovered arcade game emulation. the timing was so weird, cause a lot of the games I played back in the day were just getting emulated around that time. one of those, was Mortal Kombat 2. by my senior year of high school, then MK3 and CPS2 followed. so that's when the obligatory reflective shootout began between the two series...
if you want complexity and depth, and an overall polish that's so gleaming and sparkly that it blinds you, then Street Fighter and its off-shoots is where it's at. Capcom took the concept started with Karate Champ and Yie-Ar Kung Fu and made it not suck (which is further debatable because SF1 did in fact suck when you consider the laggy controls) and perfected it with Street Fighter 2. you can joke about them releasing the same game 5 times, but what Capcom was actually doing was cementing a legacy in the fighting game world by continuously polishing the game over and over until it was perfect. while I don't agree that Super Street Fighter 2 Turbo was Capcom's finest moment, there are millions of people that do think that.
Capcom really did some magical things with the Alpha series, because it took all the depth and added new features and corrected SF2's long standing problem by making the game flow so much more fluidly. Super Turbo was not the definitive game in the series for me... for me, it was Street Fighter Alpha 3. it had a massive roster that didn't skimp out on anyone's favorites and implemented the 3 fighting style system, and its overall presentation was just beautiful in the art and sound departments.
in arcades, I only got as far as Mortal Kombat 2 in regular circulation. I played MK1 and MK2 with an obsessive pattern. memorizing everything in MK1 was easy... it was "just" 7 characters. but with MK2, it went beyond the 7 up to 12, and instead of just fatalities, now you had the silly friendships, babalities and stage fatality moves to all remember now too. I would study the strategy guides all hours of the day to have a vast knowledge of all of that stuff, because it felt like the cool thing to do at the time of being the ripe age of 11.
what Mortal Kombat lacked in the areas of precision and depth, it compensated with the gimmick of blood and gore. I think even Ed Boon would tell you that. with the advent of the internet some time afterward, it was revealed that Mortal Kombat wasn't devised to be a serious contender to Street Fighter 2, but rather a small project that the Williams/Midway guys got to do to more or less create a response to it. what they discovered was they had a mass marketing phenomenon. the small project blossomed into a monster. Mortal Kombat 2 is widely considered the finest moment in the franchise, and while I give equal love to all the original 4 games, I have to tend to agree that yes, MK2 was where it was at.
with MK3, the expectations riding on it were extremely high. and in the grand scheme of things, it did fail to deliver on many levels. Killer Instinct creeped into the domain along with many others around the same time... it wasn't just a Street Fighter vs. Mortal Kombat world anymore. each game had a different fresh perspective to them rather than all the SNK Street Fighter wannabes. MK3 tried to be revolutionary with adding the combo craze to it in the form of dial-a-combos, but it wound up actually restricting its depth rather than expanding upon it. Mortal Kombat as a whole is not known for being a "combo" game, unless you factor in weird exploits and glitches and standing punches to lead in to other hard-hitting moves.
Mortal Kombat as a whole just doesn't flow like Street Fighter as a fighting game. Mortal Kombat however created an entire mythos of character backgrounds and storylines that all of that took on a life of their own, and lent to a massive expansion with the PS2 and Xbox games that followed.
so, if you want a "deep" fighting game, Street Fighter and its ilk wins out, handily.
if you want a complex story with a cool bloodsoaked atmosphere, then Mortal Kombat's for you.
and if you want something that crushes everyone with no story at all, then there's Killer Instinct.
in reality though, there's room for all of them. I don't really view any one series of games as being better than the other, they all offer something different, and variety is good. additionally, I'm also a sucker for Tekken, Tekken Tag Tournament is another one of the games I own. try doing what I do: beat SFA3, MK2, Tekken Tag, KI and KI2 all in one sitting one after the other.
EDIT: this apparently is my 2500th post on here. what a good one to save it for lol