Hi,
I have used ABRSM for three years for my students taking singing, music theory and cello exams. It was the exam board I was examined in growing up. ABRSM are pretty organised as an exam board and their syllabus’ are easy to use for teaching and system is easy to submit students for exams.
I have also used for two terms-LCM for Pop Vocals and Musical Theatre grades. I really like both syllabuses and it has opened up a lot more repertoire for students that really prefer to ‘perform on stage’ and who really want to do musical theatre songs and pop.
I have only had one negative experience with LCM, and this was with the first student taking the exams. Since all students have thoroughly enjoyed them. On reflection I believe they did not work hard enough. Their systems are not so slick as ABRSM but still okay. The chief examiner always responds promptly to any questions I have.