The one that fires when you want it to.
I am old enough to see every type of firearm fail to function. More often that not there are two major causes, what the shooter tries to feed them or how they maintain them.
From “fixing” or “improving” things that don’t need to be messed with, to “over” maintenance and improper reassembled firearms. Lots of stuff is no fault except the person that is operating them.
Along those lines, the most reliable firearms I have seen are single shot break open, manual eject firearms that are not “user serviceable” as far as taking them apart to otherwise messing them up.