To be honest if you're doing further maths universities will already respect your maths skills regardless of the exam board. I do edexcel and haven;t had too many problems, the textbooks are pretty useful and the exams are doable (getting 90% in all is possible, I have done so for most) if difficult (it is further maths after all). So I;d recommend them, but I have no experience of the other boards really, and they are all pretty similar.