Finishing the physics graduate curriculum as undergrad
Research experience is almost always better than additional classes, even graduate classes. Either graduating early so that you can work/volunteer full time in a research lab or taking the minimum number of credits to maintain your status as a student and work/volunteer part time in a research lab is likely going to increase your chances of admissions to a top graduate school much more than taking a full load of classes.

If you go with taking classes, classes that fulfil general graduate requirements are going to be less valuable than classes that will help prepare you for your research.