Depends entirely on the subjects. It would be better to get As in maths and physics and Bs in further maths and chemistry than AAA in maths, physics chemistry and a c at AS English Lit or something if you wanted to do maths, physics or engineering for example
On the other hand if you wanted to do medicine it would be better to get As in maths, chemistry and biology and a C in AS physics than only two As at A2 which might make admissions tutors put you in a seperate (lower) pile.
UCAS points in offers are usually limited to three subjects anyway, so two Bs might not be more points than one A, but dependent on subject and course, may be viewed very differently.