grind mx1, the other subjects prelim courses are basically just foundation and everything is pretty straightforward and easy with quite minimal effort. MX1 and MX2 can reallly boost your HSC if you do well, if you're good at maths they're very worthwhile. Personally I didn't find prelim mx1 very difficult (can't speak on hsc mx1 as I'm only just starting), and as a whole much more interesting than advanced.
Also, achieving a good mark in accelerated MX1 will take some of the stress off your HSC in 2024, as you've already completed 1 unit (potentially 2 if you end up doing MX2)
So far mx2 has been pretty interesting, obviously I've barely started but I do enjoy it, mx1 and 2 are more enjoyable than advanced imo