What difference does it make for getting college credit?
Calc AB is 1 semester of credit; BC is 2 semesters of credit (full-year).
Basically AB is Calc 1, and BC is Calc 1 and 2.
It depends on colleges and majors.
Some colleges allow students with Calc BC score 4+ take the second calculus class.
Some colleges allow students with Calc AB to skip a math class required for a major.
Colleges are all over the map in how they apply AP credits for math and physics. You could get 80 different answers here and they would all be correct for at least one good college.
You can look up the AP credit listings for various colleges of interest.
The situation described in reply #1 is a very common one, although there may be variants (e.g. depending on the score). But some schools have schemes which are not variants of #1. However, for the same score, subject credit for BC will be at least as much as for AB, and may be greater. The maximum subject credit will be a year of frosh-level single variable calculus (but may be less at some colleges and none at the few colleges with proof-based “frosh-level calculus”).