I think it depend what your looking for in a qualification,
becuase for A levels they go deeper into the subject and give you more understanding about it, But the IB Goes less into more subjects, and with the extra stuff it gives a broader range of skills and education.
For some people who dont know what they want to do or are just "good" at everything then the IB is better, but for people like me who are better at sciences (or humanities/ englishes etc) it is easier to specialise in the subjects you want without having ot do english (or maths... etc)
The IB is marked out of 45 isnt it?
if it is then i would say that
38 points = AAA
36 points = AAB
33 points = ABB
30 points = BBB
is roughly right, and then you have the grades of the additional AS level between the grades.
The IB is igven more UCAS point i think because it shows you are a more rounded person and have a wide range of skills which is what unis look for so it may seem better in their eyes
Opps that went on a bit long, didnt think i had so much to say on the issue!