Personally, I think it comes down to why you're choosing those subjects. If you really like Sciences and enjoy the way/method/tedious nature of studying those subjects then it's fine but if you're picking it for the scaling or because it's 'beneficial' for uni courses/med then I think you should reconsider.
I know a handful of kids who picked it but ended up regretting - it's tedious in some ways and it always feels like you're studying the same thing with no variety, unlike, say, languages.
But, if you're choosing them three because you genuinely enjoy learning it and don't mind studying for 3 subjects the same way, then there shouldn't be a problem.
Yeah basically what Jolteon said, pick the 3 sciences only if you genuinely love science, or if you don't, it will come back to bite you on your butt D:
If you enjoy practicals/hands on/making relationships to scientific concepts/love variables (imao idk) and scientific experiments above all, then choose the three sciences but you must beware there is a relatively huge workload, doing 3 sciences usually means you'll get the assessments due within the same week/period, so prepare to be stressed (eg in my school week 8 is the science week where all 4 sciences have their assessments due, some students who love science chose all 3, I don't think they regret it but it is difficult, especially if you don't genuinely love science.
Pick the three sciences if you love science, all aspects of it. Good Luck!
Currently doing 3 sciences right now (for the new syllabus too), so here's my opinion lmao. Only pick it if you genuinely like science and you're confidant in your ability to do well. For the workload, yes it is a lot (but in my opinion, not too much different compared to other subjects honestly). Just stay on top of the content (so do constant revision, stay up to date with homework) and you will be fine. However, not many people are good at all 3 sciences and this you may find an issue. Generally I would say I'm pretty good at Chem and Bio, but I'm failing Physics pretty miserably lmao (think 90s and then 70s). Despite my constant effort into physics I guess I'm just not good at it even though I really like the subject lmao. So I'm not saying you're going to be like me, but pretty much all the 3 science kids I know have a 'weaker' science, be it bio or physics. So I would SERIOUSLY consider if you are good at all the subjects (I took phys because I was decided between eco and phys, and I knew I would drop whichever I picked for 4u eng so it didn't matter much to me, but phys would help to chem more) so that you won't have to have trouble with not enough units in year 12.
Work load isn't bad in my opinion, but there are the depth studies which are a pain in the ass especially if get them at the same time, but with good organisation you should be good.
My opinion on the subjects:
Bio- Mod 3 and 4 was too boring for me (ecosystems and biodiversity) because its literally geography lmao. Mod 1 and 2 are ok, a bit repetitive though. Probably the most writing and heaviest work load to stay up to date for me (due to the sheer amount of content and note taking), y12 syllabus is defs better tho (viruses and diseases !!)
Chem- not bad, mole concept was super confusing at first but once I understood it makes a lot of sense (but took me ages to get my head around bc I'm slow asf lmao)
Phys- you either hate it or love it, very conceptual as well. you either get it or you don't. lots of calculations and a good understanding of maths to do well
IMO- definitely take chem but only take bio if you are genuienly into the subject (people who take bio just to do 3 sciences will generally do bad bc they aren't interested and despite people saying bio is easy, they mark super harsh and theres a ton of content) and only take physics if you geniunely like the subject + are good at math/coneptual subjects with formulas (otherwise you will struggle like me lmao)
3 sciences is fun though and I have no regrets picking the subjects i did, just make sure they are right for you too!