I went to both, and my rank went up from bottom in year 11 (from going Matrix (((
I went there from year 7 onwards ) to top 5 in early Year 12 (from going Sigma!!!)
Matrix was alright, however some of the tutors were super questionable when it came to explaining things, which is probably why I completely died in my prelims. I don't really remember much from my hsc year tbh lmaooo but Sigma put more emphasis on how I should be answering/approaching different questions which really helped me/stood out to me!