I'd say passing or first touch. It's hard to say which is more important - if you've got a team of players with great first touch but they're shite at passing... they're not going to be up to much. If you've got a team of great passers, but they have a first touch like Lukaku (tbh, I think Lukaku is actually a great passer of the ball... and he's got the touch of a rapist)… so you've got a team of Lukakus, then they'll be able to pass the ball but they'll give it away constantly.
I'm inclined to think the side that can pass the ball better would win that. It's hard to imagine a side where they're only really strong at one technical attribute though, so it's a bit of a silly hypothetical.
The most important physical attribute is stamina. The players that get tired very quickly, I always end up rating less, because you can't rely on them for 90 minutes.