Since it has not been confirmed that you can transfer your character from old to new gen Id say its best to start on the new gen if possible. I'd hate to have a thousand hours on Destiny 1 xbox360 only to find out Destiny 2 is xboxone/ps4 only and there is no way to migrate your character. And let's no kid ourselves, Bungie would have to be outright stupid to continue to make xbox360/ps3 versions after Destiny 1 due to serious compromises they'd have to make to the one/4 versions. I'd really hate it if the maximum PvP match size five years from now was 6v6 because the 360/3 couldn't handle anything more.