I have done both. A levels, personally, were dull and just generally unenjoyable. I did Chemistry, Biology and IT, and as I didn't want to do IT, it didn't work out particularly well for me. I had no interest in the subject whatsoever and, although I put effort into it, it was nothing compared to the effort of Chemistry and Biology. Now to do my A levels, I stayed in my secondary school, which was a huge mistake. My Chemistry teacher was new for starters and didn't have a clue about what modules we were doing and so her teaching was appalling. I failed the AS exams of Chemistry and IT, so I thought I might as well quit now and do a Btec instead.
I did a Btec in Medical Science, which was basically Chemistry, Physics, Biology and Engineering and I absolutely loved it. Biology was more "hands on" than it had been when I had done it as an A level and Chemistry was much more enjoyable because the teacher actually KNEW what he was talking about. There was still a lot of work involved but because I thoroughly enjoyed the subjects, I found it wasn't a chore to do. Btec is not as hard as A levels for the simple fact that there are no exams whatsoever, but it is certainly not a walk in the park either.
Yes. It's offered to those who fail their GCSE's at my school 6th form.