Definitely preferred A-levels to GCSEs but I'm not sure if that's down to my overall sixth form experience being better than secondary and having amazing tutors. I feel as though I had a lot more freedom during sixth form with the material I wrote about (in English Lang/Lit and History) with coursework and exams, which I didn't feel during GCSEs. With A-levels, I was able to showcase my writing properly as it was tailored to my skills and not mark schemes.
That, in turn, prepared me for uni.