Skill being something that you need to practice to master, ability meaning "born with it".
I have to say ability for sure. I can go months without playing a game, come back and play, and make it seem like I last played the game yesterday. I.E., do very well. Meanwhile, there are many high prestiges in this game (It's assumed with all the playtime they'd just naturally get better) that either have below a 1 K/D, or hardly above a 1.
What do you think?