Well I will continue to enjoy my nostalgia biased view.
I can remember back when SFI came out. The cabinet (I still think it is one of the best all time dedicated cabs), the pneumatic buttons were mind blowing to me back then. The game itself...I hadn't played anything like it.
If you have the two next to each other yes SFII is going to be superior in many ways, if for no other reason...TIME.
THe second is exactly the same as the first really. Ryu/Ken are the same, they are pretty much unchanged, Sagat is basically the same. The plot of the game, the gameplay, the set up the story, they are the same. The second is just some new characters with updated graphics. The first one started it all.
As far as controls go, well I could do the special moves fairly reliably in the fist one and had trouble for the longest time on the second. I have found an SFI since and had trouble doing the moves again. On the first one try going much slower and letting the joystick return to center right as you hit the button I find and for some reason doing the fireball with Jab punch seems to work better...maybe it is just me, but with practice, you can get it reliably. They are definitely not the same game when it comes to doing the special moves.
Here is a guy who has little to no trouble doing them:
http://www.youtube.com/watch?v=181bEWh0KqI&feature=related
Either way these are all just peoples opinions. If given the choice, I would gladly take SFI with the original dedicated cab and the pneumatic buttons any day, over the most converted game in the history of arcades. It would be a museum piece to me. To play day-to-day, I would probably take SFIICE.