Welcome to the club! I love people who love maths

Honestly though, I found most of further maths dreadfully boring and mechanical. Conceptually, some of the content was nice, like statistics and trigonometry; but they were still quite dry because of the focus on skills and computations rather than understanding. On the other hand, you learn mostly practical stuff and since business maths is part of core now that's two-fold.
If it's your ATAR that's most important to you though, I'd recommend further maths over methods. There's less content that's less difficult and it's a lot easier to maintain your ranking in most cohorts. It scales down but at the high end you probably wouldn't even notice it. It's probably important to note that a good portion of questions on each of the exams will be written with the intent to still confuse people who do spesh and methods, so it won't be a cake walk no matter which subject you choose.
Obviously I still recommend you do something you enjoy, and if you think you'd enjoy repeating methods (on the new study design) more than doing further, definitely do that. Is there any reason, given that you like maths, that you aren't considering spesh?