The original question asked about which is your most trusted gun or more specifically:
Which gun (or guns) do you trust the most?
it did not ask which is your most trusted ammunition. Going with that in mind, I would choose a bolt action rifle from among my firearms. I have a revolver, semi-automatic pistols, a pump action shotgun, lever action rifles, semi-automatic rifles, and bolt action rifles. The bolt action rifles absolutely have the most reliable actions of them all. A .22 caliber bolt takes less abuse than a higher caliber, so if I had to choose the most reliable firearm that I have it would be a .22 LR caliber bolt action rifle.
Of the bolt action rifles I own, it is a toss up between a Remington 513T Matchmaster and a Mossberg M44. They operate flawlessly. They feed every ammunition type flawlessly when clean or dirty. They are wonderfully reliable firearms. Of course you can think along these lines:
If it really must go "Bang" it wouldn't be a 22 - I've had too many fail because of the priming compound not being consistent in the rim.
Then again, I have had very few failures to fire with rimfire ammunition; probably about the same percentage as with centerfire ammunition and, that is not much. Oh yes, centerfire ammunition fails too. Even the fairly inexpensive (not the cheapest stuff maybe) rimfire goes bang for me 99.9% of the time. If it is the ammo that is faulty, it does not make me trust the firearm any less, it makes me trust the ammo less or the combination of the two less. If the ammunition does not go bang because of a fault in the ammunition, it does not make the firearm any less reliable, it makes the ammunition less reliable. If you seem to be getting ammunition like that there could be some causes such as: poor quality ammunition - remedy: buy higher quality ammo; dirty firearm - remedy: clean it; worn firing pin or weak firing pin spring - remedy: repair it.
Which one always goes "bang" when it's supposed to?
Of course, I also have some bolt actions in higher calibers. I own a couple of Moisin-Nagants, M44s. They are pretty reliable but I cannot imagine myself thinking that these are more reliable than are the two .22 rifles I mentioned. They are surplus com-bloc military rifles; this implies com-bloc military care which in my mind is not the greatest. They also fire a pretty heavy duty round which pounds the heck out of them. Sooner or later this is more likely to lead to a problem in the mechanics of the firearm.
Which one do you KNOW you can count on if and when you need it?
Well, if you are selecting a firearm that you can count on, you should not rule out a choice because of something that is the fault of the shooter.
Autoloaders can stovepipe...pump shotguns can short cycle...a double-barrel holds only two rounds...etc.
Most stove pipes that I have witnessed are due to dirty guns and or shooter error not due to faulty ejectors as some may suspect. If a pump shotgun "short cycles" it is almost definitely because of shooter error. As far a double barrel gun only holding two rounds, that does not make the firearm any less reliable, that is simply a design feature of the firearm. If someone chooses to use a double barrel shotgun as a primary weapon in a firefight, shame on them if they need more than two rounds and cannot combat reload in time. Again that would be shooter error for choosing the wrong gun. That is not something that should make the gun any less trustworthy.
Now back to this specific question for a bit:
Which one do you KNOW you can count on if and when you need it?
As for counting on it when I need it, I would choose a firearm design that I know would to be dependable. I would choose a firearm that was quite versatile. I would chose one that I would know to be inherently strong because of its basic design. I would choose one with which I have experience enough to realize that the particular firearm fits those other criteria.
If this particular question had been asked in the realm of self defense guns, big game hunting guns, birding guns, and so on, I might have chosen differently. As it was asked, quite in general as to which 'do you know you can count on', I would definitely opt a .22 LR bolt action rifle as the most trusted firearm I own. Combine one with high quality .22LR ammunition and then the combination is quite trustworthy.
All the best,
Glenn B