Which raid would be least overwhelming for a first run?

The group can make as much difference as the raid. Look for a teaching run that says beginners are welcome, then ask which raid they’re doing and whether they’ll explain each encounter as you go. A patient group is a much better starting point than joining a random run that expects everyone to know the mechanics already.

I’d pick one raid and learn it in small chunks, rather than trying to memorize a full guide first. A short overview can help the names and basic goals make sense, but it’s fine to ask for the explanation again once you’re actually in an encounter. Let the group know up front that it’s your first raid.

If the social part is what feels daunting, say so when you join. You don’t have to be an expert or keep up with fast instructions on your first try. A group that’s willing to slow down and answer questions is a good fit. If people start making fun of you, find another group.