Which transcript would look better?
Student X
AP USH - A
AP CS - A
AP Calc BC - A
AP Physics C - A
Spanish 3 - A
Amer Lit - A
OR
Student Y
AP USH - A
AP CS - A
AP Calc BC - A
AP Chemistry - A
Spanish 4H - A
Amer Lit - A
Assume both students are planning to study in the comp sci major in college
Which transcript would look better and is it true about what they say about AP Physics C and Calc BC that they are two special classes that look good on college apps…
These two are almost essentially the same. What science did the students in question take the year prior? Is one one year ahead in a language? Or did they override into it? What about AP scores? Does one have more ECs? Which one has the better overall GPA? What are they taking next year?
AP Physics C vs. AP Chem will be viewed identically by colleges; both are amongst the most rigorous AP classes.
Spanish 4H is obviously preferable to Spanish 3.
Who are “they?” Colleges want its applicants to take the most rigorous courseload they can handle and perform well in. AP Physics C, while demanding, is not viewed as being “better” than AP Chem or AP Bio. AP Calc BC is not viewed as “better” than AP Calc AB, particularly if the school does not offer the former.
I agree with skieurope in that AP Physics will not necessarily be looked upon more favorably than other AP science classes. Take whats most interesting to you. However, I will disagree with what he/she said about AP Calc BC not being viewed “better” than AP Calc AB. BC is significantly more difficult and fast paced than AB, and will be more reminiscent of how well you do in college level math classes. Obviously, if your school does not offer BC it will not be held against you, but if it is offered I strongly recommend you take it. This is especially true if you are going to be majoring in a STEM field.
Yes, but I was forced to take AP Physics C… for the 2015-2016 year. When I requested AP Chemistry, they told me on the last day of school, that I won’t get AP Chemistry and they put me in AP Physics which was the only class left. Wouldn’t colleges understand that if I got a B, it would have been b/c the course is difficult compared to AP Chemistry, or do they assume that the two are equal in difficulty? Those grades are just the best case scenario… But I don’t think that I can get an A in AP Physics, but I am sure I can get an A in AP Chemistry. Is there anything I can do? Or am I just screwed…
Would colleges understand if I got a B in AP Physics? Or would that look worse than an A in AP Chem?
Not necessarily. Each school can structure the calculus sequence as it sees fit. The are plenty of examples where a school will offer Calc BC as a one year course following one year of Calc AB. If the school offers a one-year BC course that includes the AB topics, yes, it will be faster paced than a one year AB course. Regardless, students get into MIT having only had pre-calc, so I stand by my earlier point that BC vs. AB is not going to sway an admissions officer appreciably, if at all. Others may have their own opinion, but you know what they say about opinions… 
Will they “understand?” No. What’s to understand? A “B” is a “B” regardless of what class it’s in; you don’t get a pass because the “B” is in AP Physics.
Yes, a “B” in an AP class will always look worse than an “A” in an AP class, regardless of the subjects involved. The good news is that an acceptance or rejection will not be based upon one “B”.
For starters, breathe. Don’t anticipate worst case scenarios before school has even started.
The question is how you may have the options between Spanish 3 and 4H? I would understand if 3H and 4. Anyway, you should choose the language level that fits you. Consult your Spanish teacher.