My understanding is that braking is a system, so the caliper, rim, pad and tyre all come together to determine how well a bike brakes.
I have TRP 957 deep drop calipers (about the best deep drop ones I've ever used) on my road bike with SwissStop pads. I clean the rims after every dirty ride.
I have never tried direct mount, but as above hear good things.
If it is road you are looking at and money is no object, HED do a "Jet Black" (or similar name), that by all accounts provides a noticeable step up from any other rim. They come at a cost though.