The stopping system on a bicycle typically consists of several components working together. Those parts are the levers, calipers, pads, housing that holds either a cable of hydraulic fluid, and the braking contact area in the form of a rim or disc rotor.
In the rim brake era, compatibility between brands, models, and styles is rarely an issue though some mountain bike brakes, particularly V-brake designs, are not compatible with road bike brake levers. While compatibility across brands has been reduced in the rim brake realm, it’s nearly impossible when using rotor disc brakes. Reservoirs, pistons, fluid, fittings, and more mean that the only aspects of brake systems that might be cross-compatible are the brake pads and the rotors. If looking for hydraulic disc brakes to work with mechanical levers, Tektro’s TRP brand HY/RD hydraulic caliper brake is a popular solution.
With rim brakes, getting the correct pads, cables, and housing can improve performance. With rotor disc brakes, installing the proper pads, adjusting rotor size, and changing the model, are where the performance improvements can be made. Shimano and SRAM, like every brake company, offer brake pads with their brakes. When replacing brake pads, there are two main types of brake pads; semi-metallic and organic. And, when you're brakes are dialed, check out our primer on improving braking skills and perhaps re-think which hand controls which brake.
Shimano offers both rim and disc brakes. For rim brakes, there are now limited options to road bikes only. With discs, they can be found for all disciplines, with many of the Shimano MTB brake calipers crossing over to road with some rebranding. Their disc brake options are both hydraulic and mechanical. On the MTB side, Shimano frequently offers both two- and four-piston options, with the latter being more for gravity disciplines, including the SLX, XT, XTR, Zee, and Saint line of components.
For years, SRAM teased hydraulic rim brakes for road bikes. It’s gone now and might have been a gateway drug of sorts. They still offer rim brakes inside pull and cantilever options—their Shorty Ultimate ‘cross canti’ is one of the best cantilever brakes ever. But the bulk of their offerings is the rotor disc variety for road and MTBs.