For me it was probably Tekken 3. Before that I spent most of my time with SF so it took me a while to learn the different timings, multi-press combos and to react to different things etc, but in the end it really improved my execution and reaction. That was more than 10 years ago though and these days I’m completely hopeless at fighting games.
Oops accidentally posted into wrong forum. Mods please move to Fighting Game Discussion.