A level maths is a bit better, but still largely dull unfortunately. Further maths is a lot harder and more engaging, so if you are interested in maths I would recommend it, not to mention unis love fm. Also if you take fm, the nornal maths a level will be so trivial you don't really need to spend much time on it. If you are applying for computer science related degrees, it would be good to have the a level in CS, but is entirely uneccessary if you put in the time to improve at Cs in your free time. The a level Cs is very bad and you really don't learn that much. For the most part, unis couldn't care less about your fourth a level if it's not related to your subject, so if you are looking to be a strong applicant I would recommend trying to pick a levels related to what you are applying for. That being said, you should choose subjects you will enjoy as that's what you will be best in, so just try and factor everything in.