Since you are asking the question you already realize that there are tradeoffs. I suggest that you speak (personally) with each of the PIs giving your concerns. It might be that the "great" PI can suggest something you like.
I also suggest that you investigate, if possible, perhaps by asking, what has been the future of students mentored by each of them. A department chair might also be a good source of information on this. If on or the other has a better record of advancing students then that might be an important factor.
Two additional points. First is that any undergraduate research experience is valuable for doctoral admissions since it is relatively rare, though maybe not in your field. Second is that you aren't locked in to a particular research direction by what you do as an undergraduate. That would be especially true in the US, but perhaps less so in some parts of Europe.
It is good to be able to do something you really like, but at your stage there might be other, longer term, considerations. At the end of the day, however, you need to be comfortable with yourself and your decision. The "easy" path may not be the best path.