If you have finished genbio 1 and 2, gen chem 1 and 2, and Organic 1 and 2 by the end of your sophomore year you should take it then.
This is your best option because you have the whole summer to study for it without being stressed about having to apply, the material is relatively newer to you than it would be after your junior year, and if you mess up you still have a whole year to retake it.
If you wait til your junior year summer you will not be an early applicant and if you mess up you will most likely have to wait another year to reapply