Glock with a properly tuned trigger. And I don't think a Glock can be beat for out of the box reliability, either.
Straight out of the box and into a torture test, I'd put a Browning Hi Power, M&P, and a Beretta M9 against the Glock any day where reliability is concerned. Not saying a Glock is unreliable, just saying it's not the most reliable pistol in the world.
Beretta has a pistol at their factory that they've been running a test to destruction on for a few years. It has over 160k rounds with zero malfunctions and still going; and it's independently verified.
The Beretta has a bit of an advantage having served with the US Military. They got the US Military to test and improve the weapon to a degree that no other pistol on the planet has been tested to.
Despite it's unpopularity and it's early flaws (let's not forget that at that same time, Glocks were going through some rather significant issues), the M9 is probably the most reliable pistol in the world right out of the box.
I'm looking very forward to the next service pistol tests to see how they stack up against the benchmark M9.
