Imma say Real Madrid. Lol, PSG are not letting go of him that early, he'll be 23 then and Neymar will be old. However, I fear that Ligue 1 will stunt his development just like how it did Veratti because it has no competition. We see time and time again on how PSG get exposed in the CL. Imo opinion Mbappe did the wrong thing choosing PSG over Real Madrid. I know he was chasing the bag, but he would have eventually got the salary he's receiving now at Real within like a year.
Also PSG will prolly not let go of him unless the CL is won.