Can vouch for Ngo and Sons as I went there, but I do believe both Du and Ngo and Sons both have accelerated systems which are designed for people who joined in Yr 7/8 so they might be already 5-6 topics ahead of the current school topic. Please keep this in mind when registering for either if you aren't particularly looking for 'accelerated' tuition. I do believe there are non-accelerated options available at Ngo and Sons though.
Currently attending Ngo and Sons and Andrew's right, there are accelerated (Module 1) classes and non-accelerated (Fundamentals) classes, I think there are also further accelerated classes (Module 2, 3) which you can read about on their website. I only started going to tutor this year (which was very shocking to Dr Truong because apparently I should've started going to tutor from Year 2 lool wtf) and was put into a Module 1 class as it was the only one that would fit into my busy "schedule". Was told I also needed to attend a Fundamentals class that was free of charge to catch up on some of the topics already covered in my Module 1 class.
Basically, I ended up dropping the Module 1 class and cleared my schedule to start attending the Fundamentals class permanently. Even then, that class had already covered around 8 topics that I missed out on since the class had already started from August last year. Anyhow, I think Ngo and Sons is pretty good but there are some concepts in previous topics I missed out on that are in the current topic we're learning so it makes it difficult for me to understand sometimes.
From what I heard Dr Du is expensive, unlike Ngo and Sons (which is only $330 per 10-week term, 5 terms in total) so if you're looking for a cheaper option, I suggest the latter option. But besides that I can't really say anything about Du because I obviously haven't gone there.
Hope this mess of a reply helps you in choosing which tutor is best suited for you!!
