Depends on you and your fighting game level. Street fighter would be the easiest to get into. Characters have normals, 2-3 command normals, and no more than maybe 10 specials per character to learn. You can jump in and make cool stuff happen if you’re a masher, you’ve got a robust world tour story mode, create a character, old school games to play on rotation like final fight, Super SF2 turbo, and magic sword to say a few, and more. Definitely going to be amazing for any skill level.
Tekken will be FUN but mashing as a novice won’t reward a novice unless you pick Eddy, Alisa, or Lucky Chloe assuming they get announced. That’s it. the hardest to master by far but gives the greater sense of accomplishment when you do master the game IF you choose to take it that far. An intense high level tekken battle is unmatched by any other game. Don’t get me wrong, high level street fighter can be hype as hell, but high level tekken had you on the edge of your seat because of the sheer number of possibilities someone can use to attack or counter with. Tekken always has an extra mode like a tekken force it bowling, but they have never been on the level of street fighter 6s world tour mode.
I will have both day one. Played in both SF6 betas and have been playing since fighting street as a kid. Been playing tekken since…. Tekken. I love them both and can’t see how anyone could choose like the other is trash. If I could ONLY get one it would be Tekken….but I’d cry nightly.