Hey HappyMe!
The first thing you may want to do is decide if Methods is needed as a prerequisite for courses that you are interested in. If it is, I highly suggest taking Yr 10 Advanced maths. In regards to helping with your ATAR, any subject that you are passionate and enjoy (rather than despise) will essentially 'help' your ATAR.
I personally say go with Advanced Maths because if you realise later on that Methods is something that you do not need (or no longer interested in), it is quite easy to change to Further. You can do 1/2 Methods and if you feel like you do not need it, you can switch to 3/4 Further and it is definitely manageable! You can also do Yr 10 General Maths and still go to Methods if you want, however, once you start with general/further maths Unit 1/2 and all of a sudden you want to do methods 3/4, it would be much harder (and not advised).
To sum it up, if you do advance maths, you can still do Further no problem. If you do Yr 10 general and decide you want to do 1/2 methods, you may find there is a slightly bigger 'leap' between Yr 10 general maths ->1/2 methods in comparison to Yr 10 Advanced Maths -> 1/2 Methods (But still possible!). Hope that helps!