I have had Shimano XT and XTR , and recently the SRAM RSC brakes.
The Shimano brakes have really good bite, the XT lack any real modulation though.
XTR brakes solve that issue at a premium price, and are very well engineered and finished.
A plus for the Shimano is the ease of bleeding, and friendly mineral oil fluid.
SRAM Guide RSC.
Very good adjustability and excellent modulation.
Not the ultimate in bite for emergency stopping
All very nice, for me the SRAM Guide would be my choice though, just nicer to use.