In choosing a postdoc, how should I prioritize mentorship versus research opportunity? I am an experimental physicist looking for postdocs in applied physics and materials science. In choosing groups to inquire about a position, I am trying to determine how to prioritize potential mentorship versus potential research opportunity. I see large "super" groups with huge numbers of postdocs and students. These groups have a high potential for research with lots of funding. However, I am worried about entering an ultra-competitive environment where I will receive very little mentorship from an advisor. I am wondering if choosing a smaller group will have an advantage because of receiving quality mentorship, despite the fact that the research topics might not be as leading edge or popular.
I think that the choice of mentorship versus. research opportunity* entirely depends on your own way of working/your preferences.

If you are very good at working independently, enjoy working on your own and have the ambition to become a full professor then I would pick research opportunity over mentorship.

If you need or desire a lot of guidance, or flourish when you have lots of discussions with someone 'higher up' and you don't really care whether you do cutting edge science or just good science then you might be better of going for mentorship over research opportunity.

*As a sidenote, mentorship and research opportunity don't have to conflict necessarily. There are small research groups with excellent mentoring that do very cutting edge science