I think you should look at the graduate rankings of JHU vs UVA in Chemistry and Physics. This is because as an undergrad, you will be exposed to graduate students (TAs) and professors in your chosen field who determine the quality of the graduate program.
Although you are only considering the undergrad program, from an academic point of view, it might be important that the research opportunities around you are vast and well funded. At a higher ranked school, this may be a stronger example.
Since I go to UVa, let me tell you in detail, its physics and chemistry programs.
I am a physics/chemistry double major, with a math minor. With Chemistry, you can either start with the 40 series (for premeds) or start the 80s series (Honors chem/for majors). The 80s introduce you to O-chem by the second semester of your first year and wrap it up by the first semester of your second year. There are several different specializations within the chemistry major: biochemisty, physics, education, etc. You can also get a distinguished major in chemistry. This requires that you write a research paper at the end and present it to a panel of professors.
It is extremely easy to get involved in research. Most of my friends, who have done well in a chemistry class, have walked up to the professor at the end of the semester, and asked to do research with them. I'm confident to say that 8/10 times, the professor will agree. If the professor disagrees, it's more of a lack of lab space than of a lack of confidence in your abilities.
Also, if you do extremely well in a class, you can also ask the professor to let you TA the class in the future. This is an amazing experience. You get paid and you learn so much more about the subject, all as an undergraduate. For example, I took the 80s series in chemistry and TAed O-chem last semester.
The Chemistry major is very structured and organized but you can certainly finish it in less than four years and do many many other things at the same time. I think this applies to anyone with enough dedication. If you plan to go to graduate school in chemistry, you'll almost end up somewhere amazing (in the top 5).
Here's the website for chemistry:
http://www.virginia.edu/chem/undergraduate/
For Physics, the BA is much easier to get than the BS which will take the entirety of four years with little room to do other things. The professors are absolutely amazing. They are available, approachable, and fairly laid back about due dates, extensions, etc. The TAs can be a bit annoying sometimes because they are not well prepared.
Research is also very easy to do. You would just have to do well in a class, get to know the professor, check out his research interests, and if there is a match, then be brave enough to approach them. You can also get a distinguished BA in physics, which requires a research project.
http://www.phys.virginia.edu/Educati...MajorBrochure/
Also, if you carefully read the major requirements in both fields, you'll see that as an Echols scholar, you are given exemption from a lot of unnecessary, but area requirement classes. This exemption allows you to have room for other interesting and relevant classes in the very beginning. What ever you decide to major in, you can pick a professor to advise you in that field.
That's what I can say about the two majors at UVa from a purely academic perspective.
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I don't know much about JHU except that the school is in Baltimore and that the medical school is in the top 2 for research.
However, I can tell you that Charlottesville is so much safer than Baltimore, since I have seen both. This may be important if you're working at the library until 1/2 in the morning and have to walk back to your dorm.
Baltimore is very intimidating because there is no transition between upper range middle class suburburia and literally, the ghetto; so you step from one into the other.
In Charlottesville, everyone is really nice. The drivers are lenient, the people seem less troubled by sensitive things like politics, racial tensions, socio-economic status, etc.