My 2 cents.
I have done the General Maths Further orientated subject and I will say this, It is a different way of thinking when compared to Methods and Specialist.
In Methods and Specialist, I guess you think quite 'hard' on each question, trying to decipher and understand what you're being asked, within a given real life scenario.
In Further, It is more 'direct'. If that makes sense? Like, I remember doing financial arithmetic and in that, we were given a scenario, with, basically, some numbers and all we had to do was apply a formula or transpose it. In saying that, it was not as easy as it sounds, I did lose marks for careless mistakes, which can happen quite frequently in Further. Hence, why you should read and understand what the question

To me, I guess you couldn't compare the subjects, contrary to what other people are saying. As they, (Further to Methods/Specialist) are different subjects in the sense on how you think. However, I did quite enjoy General Maths Further as it was actually different to Methods and Specialist and it did allow me to be more careful in my working out.
I guess Methods/Specialist feels more 'abstract' whereas Further is applicable to Commerce based subjects. (Which I enjoyed.

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tl:dr: Ask your teachers, Look through the textbooks, Make a judgment for yourself on your interests. Don't think since they're all maths, I can basically scale them like Specialist>Methods>Further, which I think is not true.