Don't pick a braking system, chose a bike as a whole. Look at the whole package and ask yourself does this bike have what I want it to have? Sometimes this bike will have disks and other times it won't.
If you are choosing a gravel bike, most times it will have disk brakes. This is because you are limited by tire size when using calipers. Gravel bikes accommodate large volume tires which necessitates disk brakes.
From the little you gave described, I would chose a bike takes at least a 32 mm tire and go from there. All bikes in your price range are good. Some will be better than others to meet your specific needs.