I strictly play 3S now, but SFIV/SSFIV seem very easy to pick up. Blazblue is far harder to pick up than SFIV since it is so slow and you can get practcie in ev en agaisnt opponents.
So while I think SFIV would be the EASIEST fighting game to get into, I would not necessarily say it’s the RIGHT fighting game to get into. It will teach you more bad habits, shortcuts, and tons of spamming the same moves and techniques over and over. It’s easy, but not GOOD easy to help you with fighting games in general. It will just teach you bad habits and actually make you WORSE at fighting games.
Try starting with the Alpha series- Alpha 2 and 3 can teach you some basic stuff and even some good execution and footsies. The alpha games are faster, goofier and have al ot of fun stuff. so you can have fun while learning. Then move up to SFII, after you start kicking some arse at that then I would say take it to the advanced step and learn 3S. I wouls skip SFIV/SSFIV all together.