A friend is about to get ESO, but has not decided what version. When they do get ESO should I play with my current summerset character or just make a new one? which option will cause the least headaches?
You should be fine to play with your current character, just be aware you might be a little stronger than theirs (but not by much).
The only conflicts that will happen will be quests you've already completed, as you won't be able to do these alongside one another and in some cases once a quest is completed there is a new phase of that area which will make you invisible to each other.
If you play different factions then you won't be able to do Cyrodiil content together, you can so all other content together regardless of factions.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."
If you plan on questing together in an area you've already done with your existing character, I'd suggest making a new one.
So you can play through the quests together. That's much more fun than just having to follow your friend around.
If you're CP level your character will always be that CP if you allocate them. Thus making your abilities of lvl 1 hit at a similar level.
To be as strong as your friend you'd have to make a new character and not allocate CP and scavenge gear instead of creating gear.
However, it might be a little more mistake friendly if you just play alongside your friend with CP. If you plan to make a new character then yeah, it might be fun to level with your friend.
As for the other posts, yes if you completed a zone and want to redo it with a friend you pretty much have to make a new character.
Help your friend out. Make him some training gear so while you two are questing/hunting he is leveling up at a faster pace to ultimately catch up to your main. And if you want to actually make a new character with him, you two could each buy the Pledge of Mara and get extra XP when playing together in a group.