Hello!
As a year 11 student who is undertaking both further and methods, I would highly recommend if you would choose maths methods. Touching upon what eloisegrace has written, methods is prerequisite for many university courses and moreover, it is a very rewarding subject if a student is strong at mathematics due to the scaling.
Further maths is also rewarding and again, touching upon what eloisegrace has written, is a very doable and easily paced subject. I personally found further easy to study ahead for and during the summer holidays, I advanced up to financial maths so I could enter class feeling much more confident.
It all depends on what your prerequisites are and where you place yourself in the world of maths. If you are more into abstract thinking, methods is the way to go. If you enjoy analysing numbers and statistics, further is your best option.