With math classes, in addition to aptitude and interest, I think a lot of how a class ends up being perceived is a function of preparation, pace, and the clarity of the teacher.
MVC, aka Calc 3, can be an enjoyable, not particularly hard, extension of what you learned in Calc 1 and 2, aka AB and BC. But this assumes someone with a decent aptitude and interest in math, getting the preparation needed from Calc 1 and 2, and a reasonably well-taught class at a reasonable pace.
Given that, first, I would not see the point of taking MVC in the summer.
Second, I don’t think colleges will think it is strange a person who was not necessarily interested in majors like Math, Physics, or maybe Engineering would take AP Stats instead of MVC as their next math class after Calc BC. Stats is an extremely useful subject for many, many disciplines.
That said, nor would I actually discourage MVC, if the student had actually enjoyed Calc BC. In part that is just because I think learning more math is never really wasted, it always contributes to your understanding of the world no matter what majors or professions you choose. But also, AP Stats is . . . let’s say a “rudimentary” stats class. Again, fine to explore an interest, but I would usually suggest then taking a college stats class anyway, possibly calc-based stats for someone who is comfortable with calculus.
Like this is sort of random, but I just looked up the Data Science major at WashU (where my S24 is a sophomore), and they actually have a Statistics for Data Science majors required sequence, and that requires MVC as a prereq:
That’s not to say your kid actually needs to consider being a Data Science major, or generally needs MVC and a stats class that requires MVC. But my point is if a person found that sort of sequence interesting, it would in fact open up more possible majors, or just being the sort of person in any field who was very comfortable with statistics and data science and such as relevant to their field. Not a bad thing in our modern world.
OK, long story short–either is fine for college admissions purposes. But if this kid enjoyed Calc BC and felt comfortable with MVC as a next step, I wouldn’t discourage it in terms of continuing their math education.