I would clearly take either, both are light years ahead of Erik. Tuchel probably represents a greater chance of short term success, but also the almost certain probability of a short(ish) tenure (no more than 3 years). I am not sure how much that matters these days, especially with a robust overarching structure in place.
Nagelsman still has some question marks over his head but definitely represents a longer term project and more stability. The question is what appetite do the fans and hierarchy have for further patience, which I feel Nagelsman would require. Tuchel also has the benefit of Premier League experience.
Personally I would go for Nagelsman and look to build over a three year period. I see him as much more likely to work collaboratively with the new hierarchy, which I think is vital to success.
But I wouldn’t complain at either.