Reliability here is defined by constant performance. It doesn't matter how accurate the watch is (I got a warning from a mod once about mentioning precision vs accuracy, but I assume you know what the difference is). Outside interferences like shock or magnetic field can come into factor.
For the first time ever after approximately one and a half year, my automatic watch ran slow. I let it unwind, gently tapped it, turned the mainspring, and it went back to normal (runs slightly fast, like most mechanical watches from the factory). This makes me thinking if I only have one source of timekeeper for some period of time, I probably wouldn't choose a mechanical watch. I don't have any "high end" mechanical. They might be more reliable (should they be?) and thus would change my judgement.
How comfortable are you about relying on your mechanicals? If you don't have a reliable time reference handy like the internet, the TV, or your mobile phone would you still pick a mechanical watch for general wear? That question implies that mechanical watches are not reliable enough, of course you can challenge it with your story/opinion/experience/etc.