I voted fighting, but really it's first person shooters. Could be both really....
I can pick up the sticks in Tekken or Soul Calibur right now, not having seriously played in years, hop on, and beat some ass. I recently just did it when me and my boy hopped on 7. We used to play for HOURS in high school, probably ain't played since. Got our characters, buttons damn near the same, combos damn near the same, specials, etc... That made us get bold and take it to ranked matches... Think we lost about twice between us, good half hour of steady matches. I've also picked up MK's latest, pinned the combos, and pulled them off with ease, with a good 20 mins of practice.
All that tells me, is it's a lot of memorization. Of your moves and your opponents. Then applying that. Very easy to learn.. Extremely hard to master. Even harder to master another master if you're playing against one.
But shooters.. Go ahead and try and hop on in a call of duty.. Playing with who knows who. Playing against some know every map nikka.. Know where to camp nikka.. Already got the best guns and upgrades, and they throw you in the lobby as a Private with him... nikka with a mic and shyt. Whole team in party chat. Strategizing during the week ass dude.
Nah it's going to take you a long time to get great. And still you're at a disadvantage cause of levels, game modes, they got this powerup, they running with this set up, they got a sniper team over here.... You might miss a year and they done hopped from 1935 to 2344 on your ass. Space guns and jet packs and then you going back to revolvers and jeeps/
I think it's easier to get good with 1 fighter in a random fighting game quicker than getting good at a random shooter... but once you master that fighting game, the top is much harder