Start Wow, first time

I'm probably in the minority here but without more info, I vote retail. Classic will not hold your hand at all, it's a pretty rough onboarding experience. Retail is a much better new player experience.

But really it comes down to what you want to do when you reach max level (if that's even a priority). Classic raiding has been described as "standing and hitting" - pretty dang casual and the entire thing was "solved" 20 years ago. Retail has both 3 raid difficulties AND mythic dungeons - infinitely scaling difficulty with a timer.

The lack of mythic dungeons is what keeps me off Classic. It's my favorite end game content and now that I have a solid group of 5, I'm having a blast pushing up my score.