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.
[EDIT]
Oops accidentally posted into wrong forum. Mods please move to Fighting Game Discussion.
Not SF4, that’s for sure. My SRK commands have gotten so sloppy due to the sensitivity of the command inputs. I would say CvS2 helped me the most. It helped with motion commands, buffering, and strict links.
I feel like I always can go back to Alpha since I can do shit in all the SF games except that one without a bit of time to get used to the movements again.
But yeah, SF4 won’t help you with shit and is detrimental to play unless you’re already really good at the other games and won’t change your input style for it.
Guilty Gear for d-pad (psp one no less, taught me how to SRK and the other motions) and Melty Blood for stick. (taught me how to combo with jump cancels and stuff and sheild system helped reactions)
I know the input system is a bit sloppy and forgiving in SFIV, but from the sheer amout of time spent in the practice mode, I’d say that helped my execution more than anything else. Time spent on Akira’s complex counter game in VF5 and working on just-frame moves in Soul Cal have also really helped my execution and reaction time.