First there is one very important factor, which syllabus are the QBs using. I tried Aviator, also very good, in chapters and everythingh, but for UK syllabus not the right questions, to many questions in each subject, and with that not concentrating about what is relevant for your exams.
ATPL teachers comments are probably the same as Bristol Forums, takes you 2 minutes to sign up, you search with Q number, copy and paste - and if one question has had a problem you get information and very good help.
Furthermore many questions give you instant INFO results of how to solve ready made worked problems, no need to wait for a "teacher" to get back to you with how to work a problem.
But listen what works for you, is good for you, I believe Bristol's QB is more updated for the UK exams, specially with relevance to the new questions in V3, many of them in UK exams now last time. I personally had great help of Bristol, and find other QB's annoying with to many questions not relevant for current exams, and most important do not have instant INFORMATION how to solve problems.
In Bristol example most calculations have worked sollutions how to solve problems, I did not find that with JAAQB.
To be honest, it easy to "take" questions from other QB's, but giving a worked example how to solve the problem takes more time and work!