It seems that most flint guns have faster lock times than percussion guns... Important in minimizing motion between the sear releasing and the powder charge detonating.
Then again, in wet conditions, I'd prefer the percussion rifle. Push on a cap, wipe some lube/grease around the cap on the nipple and it will fire even after an afternoon in drizzle or rain. Not so sure I'd be as fortunate with flint...
I've often hunted with a flintlock for extended periods in the drizzle, and have found it to be not that much of a worry. I've never had an issue with delay or misfires while hunting in moist/wet conditions, but that could be an entirely different story if the rifle was fouled and reloaded, and then left to sit for a while. It does come down to paying attention to details of course.
I just keep the lock tucked up under my arm while carrying or still hunting, and have a cow's knee that I may occasionally use while sitting. I do have the waterproof style pan on my rifle and pistol (but not on the Bess), and that helps if you get an occasional drip of water that just happens to hit the lock.
One huge advantage the flint has over percussion in moist conditions (IMO) is that I can take a momentary glance at the lock area of my weapon and know that I'll have positive ignition. A percussion lock doesn't give you that option. With a flintlock you really need three things to guarantee ignition. A sharp flint, a clean frizzen, and dry powder; all three of which can be verified with a glance and even corrected if necessary in a few seconds.
Range conditions don't accurately represent hunting conditions, at least in my experience. At the range, I regularly shoot a lot and allow my flint to get so dull until it doesn't spark all that great before I break down and knap it. Repeated shooting builds fouling, and some of that is of course on my frizzen, again hindering spark. If it's humid, wet, drizzling, or raining the fouling pulls moisture into the pan and bore, moistening the priming and main charge. I've never had that moisture prevent ignition, but if I let the loaded gun sit long enough between shots I'm sure it would... I do regularly clean between shots to keep things clean and consistent, but the gun is far dirtier than it would ever be allowed to get in a hunting situation. I have less-positive ignition at the range than I do in field conditions, because I'm not as careful with ignition details at the range.
A flint gives me 40-50 shots before it gets dull, at which point it takes a few strokes to knap a fresh edge (not done while loaded, obviously).
When I hunt, I always hunt with a fresh edge, and dry fire a few times prior to loading to verify I have a heavy spark. If the frizzen is skimmed-over with powder fouling, it can easily prevent or reduce your spark as well. Again, in a hunting scenario I just make sure it's clean. Sharp flint and clean frizzen means there will be plenty of spark...
When it comes to dry powder, that's easily verified by flipping the frizzen open. That allows me to verify that my priming is dry, and in addition I can see a kernel or two of the 2F main charge in the vent.
Dry kernels visible in both locations, along with a sharp flint and a clean frizzen means there's gonna be a bang when I pull the trigger.
And of course it's a direct line between the pan and the main charge; no corners to go around.
Percussion locks don't allow that type of verification. Even with a fresh, clean rifle you have the potential for a little bit of crud, oil, or grease in the nipple or bolster to block the spark from getting to the charge. If you have a spotlessly clean rifle, you run the risk of oil or grease, and it just takes a little to cause problems. If you fire a cap or two prior to loading you mostly remove that potential, but add the potential for a flake of soot or fouling to be introduced in there somewhere... Even during the loading process you may have some "clumping" of powder in the bolster area (I can visually discount that potential with a flintlock because I can see the kernels in the vent). I've never hunted with a percussion gun, but I have friends that do, and have friends that have missed opportunities due to those factors.
Percussion guns can obviously be very reliable, of course, but I've seen far more mis- and hang- fire issues with them as a whole than with "decent", well cared-for flintlocks. Unfortunately, many of the flintlocks on the market aren't all that great. They have poor frizzens, poor geometry, and are poorly tuned. Even good locks are often poorly loaded, or loaded with synthetic powders just adding to the nightmare. It's really little wonder that so many people are scared off by them. Even good flinters are poorly loaded in the movies so that they appear more dramatic when fired (the delay is actually exaggerated for the movies; the Patriot and The Last of the Mohican's are easy examples).
In reality, "late" flintlocks were highly refined, highly effective ignition systems. Flintlocks were in military use for how long? 250 years? The military seldom makes use of a weapon without doing some serious tweaking and refinement... Give 'em 250 years to perfect a system and it's no wonder it got to be pretty danged good. When percussion locks came into play there was surprisingly little "rush" to adopt them in the military or for home/frontier use. They were a new "fad" of course, but only saw military use for maybe 30 or so years(?) before quickly being replaced by cartridges. Percussion just wasn't the system of choice long enough to have the bugs ironed out.
The true value of percussion wasn't a drastic improvement over flintlocks, it was that the technology led to the invention of the primer.
I'm obviously biased, but I honestly consider the 1820's to 1840's flintlock to be superior to percussion.
