'Tis all very subjective Ed.  For instance, in recent past I have had 3 differnet brakes - Hopes, Shimano XT & Shimano XTR.  I can safely say that, with the same size rotors, the xtr are better than the other 2 with the XT's next & Hope's last.

Larger rotors can improve braking and it is the cheapest way to add bite to brakes that you don't feel are up to the job.

Squealing can be down to many possibilities - misaligned caliper, mounts or rotor, pad contamination, loose bolts or pads etc. The only time I've suffered it was with a caliper that wasn't set quite right which was soon sorted. If your bike or the brakes are nrew then it may b worth  visit to the shop you got it/them from for their opinion - a decent mechanic may be able to tell pretty quickly.

thanks for that I will save my money for now and deal with the squeaking and mading upgrade in a few months.