[D] Picking an ML lab as an undergraduate: big, established lab or small, focused lab?

Some background: I'm a third-year trying really hard for a PhD at a good school (a crapshoot, I know). I go to a solid school for CS and have some basics like a good GPA, plus I've been doing some applied work in healthcare at a T3, expecting a first authorship at a top medical journal.

But what I'm interested in machine learning itself, not necessarily its applications in a specific field where the cleverness comes from applications rather than …

basics big good go to healthcare lab machinelearning phd school small solid undergraduate work