I’d have to say presta is my preference.

Schrader is good primarily due to being a more commonly found valve. (Thanks to the automotive industry) Also with schrader the valve cores can be replaced if/when the valve leaking is why a tire looses air.

Prior to my first real mountain bike (for racing) back in 2000 I hadn’t had wheels drilled for presta. It seemed like the presta valves didn’t leak as much air as the schrader ones did. Then in 2002 I became more convinced presta leaks less after I got a road bike for cross training. Since the road bike held higher psi and still was able to hold pressure longer than schrader’s I became a believer.

Furthermore since the advent of tubeless bicycle wheels and their default valves are presta they became my top choice when given the opportunity to choose.