like Joel says, its the pads that make the biggest difference to brake performance. You can get decent performance from good pads on cheap discs, but you can't do it the other way round.
The best brake setup is DBA 4000 wiper slot discs and Pagid grey pads. If you're doing lots of miles, you may wish to use the longer-lasting Pagid Yellow
Group buy currently on for discs and pads combined
clicky