I've been in the same group for all of undergrad. It's been a wonderful experience, I'll have two 1st name papers in solid journals by the time I apply, and I've loved the environment. The PI is well-known, has connections, and will write me a strong rec letter, etc.
The group is a biophysics theory group, though, and that's where all of my experience is. I definitely want to do theory, BUT how do I apply to graduate school making it clear that while I loved that lab, I'm not sure that I want to be in biophysics? I don't want to weaken my app by not having the conviction and interest to continue in my current paths of investigation, but I also want the freedom to try completely different and separate realms.