I'm on ps4 btw. I don't think you need to re level characters, your progress will carry over(I think).for you, switching to Xbox one will probably be a much more convenient choice if you already bought dlc, the game, and paid for Xbox live. But overall the most important thing (for me atleast) is who you want to play with. If you would rather play with your friends on ps4, maybe go with ps4. If you prefer playing with your Xbox friends, go with the Xbox one.