Python is an awesome language, but in a HS class you probably won't get past simple scripting paradigms. If you guys were already CS students with solid programming experience as well as the theory behind it, or if you were just science students wanting to hack around, then python would be a great choice.

However, I think it would be more beneficial if you guys were to learn (sorry) Java and OO knowledge so that you could take the AP test and perhaps save time and money if you decide to move on to college.

Either way, VB.NET would be at the bottom of my list. C# would be great, but the professor might find the C-style coding too overwhelming for the students. And F#, being functional, is probably out of the question for a number of reasons.