I was also very pleased to make this discovery! If I had kept playing the Euro-version I would eventually have smashed my entire control panel in anger...
The "officially recognised as best" version of the game would probably be Super Street Fighter 2 Turbo. That's the version that gets played the most in competitions and stuff, I think. I haven't really checked the difficulty in ssf2t compared to the USA-version (ssf2tu), because I prefer the original SSF2 in any case.
I like the original SSF2 best because of the slightly simpler game mechanics, lower speed (I'm an old man), and the original colours/costumes for the characters. The USA-version also has the "FBI - winners don't use drugs"-screen, which I kind of like, and add the "correct" difficulty level, for me ssf2u is without doubt the best choice.
Good luck, SSF2 is easily one of the best arcade fighting games ever made!
