I think it varies depending on schools and students. Some schools offer hardcore physics that many students struggle in, while some people are generally strong in math/physics that they can take physics with other upper level courses. So, for your question, I would ask your peers at the same institution. They will have more unbiased answers for you when you try to finalize your class schedule.
The bottom line is that it's good to finish all the physics courses before your MCAT. For instance, if you see multiple electromagnetism passages in your real test day, your physics 2 will come in very handy.
So, in short, if you are studying for MCAT during the summer between junior and senior years and then take it before senior year, I think it's fine to take physics during the junior year. However, I agree that most people take it during the sophomore year so that they can take MCAT before their junior year. It's up to you. If you can study physics 2 on your own during the summer after your sophomore spring semester, you will probably do fine in MCAT and even find physics 2 "easier" or "more tolerable" during your junior fall semester. Some non-trads have been out of schools so long, but they still manage to study these materials on their own, so I know it's possible to take MCAT before you take that physics 2.
Just my opinion =]