The best opportunity is one where you can get an independent project in which you contribute something and have adequate supervision (either from the PI himself or surrogates such as graduate students and postdocs) that you can have a meaningful experience. You need to be able to go to interviews and describe what your contribution was, even if it didn't lead to publication, and your thoughts about the overall scope of the project. Publications are nice, but not critical, and it's better for you to be able to describe your work in the future and get a notion if PhD work is even for you.
I can't tell from what you're describing which of those experiences fits that. I'm a little confused, in fact. Is the PI leaving? If so, are your options
1) Stay in that lab and keep working on that project with the PI not around - vs -
2) choose a new lab
Or is it actually, PI is leaving:
1) choose new lab #1
2) choose new lab #2
If you're more specific, I can perhaps give you more advice.