TRP HY/RD is absolutely the easiest swap because it is cable actuated but has a hydro system built in to the caliper, so you just swap the caliper and have hydraulic brakes.
I have them on my commuter bike, I don't think they are quite as nice as a fully hydraulic setup like the Shimano XT M8000 would be but I also don't feel that the braking demands on my commuter are nearly as tough as on the mountain bike.
One note on the TRP HY/RD, for the past year that I have had them I thought they were absolutely horrible brakes! Turned out the pads that came with them were aweful, I put some cheap Jagwire pads in and brakes are quite nice now.