Technically, I think Mbappé will be much superior. The current potential is, like you said, Haaland is getting support from his Manchester City teammates. In addition, Pep Guardiola can exploit Erling Haaland's full potential. Pep Guardiola is a good teacher. But for example, Haaland alone carries the whole team like Mbappé. I bet we won't see a trace of him in the match.
If Mbappé goes to Real Madrid in the upcoming transfer season, Mbappé will develop more comprehensively. I believe that in the future, he will be a goat. But time is running out for Mbappé, and he should be decisive with PSG and not try to sink deeper into the quagmire.
My concern is whether, should Mbappe depart from PSG, he will receive the same special treatment at another club as he has at PSG. The support for Mbappe seems to be unique to PSG, and if he were to move to another major club, the authority within his contract would likely be more limited, and he would become just another player.
It's akin to Messi's move to PSG, where Messi received immense support from Barcelona, but it seems less pronounced at PSG.
On the other hand, Erling Haaland garners support because he isn't overly flamboyant. Haaland, regardless of where he goes, is likely to maintain the support of his teammates because of his exceptional qualities from within. That's why I've chosen Haaland.