I think alot of fanboy blindness is happening here.
I LOVE Mortal Kombat. It's my favourite fighting game franchise alongside Killer Instinct and Street Fighter, but all in all, Mortal Kombat is my #1. But Street Fighter has had a professional competitive scene for a loooong time, and that community have helped the devs at Capcom to make Street Fighter what it is today. The gameplay of Street Fighter is much finer tuned and more tight than MK, the tech have been worked on for alot longer time than MK, there's alot more variety in character types than in MK etc.
For professional/competitive players, Street Fighter is a better game.
Mortal Kombat has only just recently with MK9 entered that scene, but MK as a franchise offers alot more when it comes to the more casual gamers. They offer stories and lore that, for a fighting game, is pretty deep and varied, the gameplay is easier to go at for a casual gamer, the many modes in the games like the mini-games, Konquest mode, Story Mode, the many Towers, the Krypt etc., they are all there to attract casual gamers. Even the main things Mortal Kombat is known for, such as the blood and gore, the Fatalities and various other finishers - they are all there to attract casual gamers!
I'm not a pro or competitive player, so all those things speak to me, while a game as Street Fighter seems more intimidating to me, because it caters more to the pro/competitive community and they've had so many years to build up this image. Mortal Kombat hasn't.
So for which one is better of the two - they cater to different parts of the fighting game community, so it depends on what perspective you are watching at it from. But there's a reason Street Fighter is one of the top popular fighting games world-wide, while Mortal Kombat has taken a backseat compared to it. Yes, MK is known and popular, but
not because of the gameplay, but because of the aesthetic choices the MK team made when making it.
All that said... I think it is awesome Mortal Kombat has with the two recent games made more of an attempt to make MK appeal to the more competitive community, but it is still very new on that scene where Street Fighter is a veteran. And there's no denying that.
Sorry for the long off-topic post.