For what it's worth, I work in 911 dispatch, so I've heard pretty much every reason someone could call the police, some good, some not so good, and there's always weird exceptions or edge cases where a situation that I normally wouldn't personally think warrants police involvement can get tipped over the edge (regardless of whether I think they're needed or not, if someone calls asking for police, I'm dispatching them, if the cops want to ignore the call, that can be on them)
My general rule for fights/domestics, is I'll call for situations that are or look/sound like they're about to become physically violent, neighbors yelling at each other next door-not my problem. If I start hearing them throwing things around, I start hearing mention of weapons, they're suddenly out in the street, etc. then I'll call.
I'll also call when it's just a verbal argument in a situation where that sort of behavior is totally uncalled for, like an irate customer yelling and screaming in a store, manager is asking them to leave and they're refusing.
Or if I witness a crime where the victim is a person, small business, or public property.
Situations where a person is or might be in significant danger or distress.
Reckless drivers if they're really excessive, not your run of the mill bad driver or asshole speeding and running shop signs, you need to be a couple notches worse than that- swerving all over the road, or speeding to a ridiculous degree.
Certain road obstructions and other traffic hazards.
When in doubt, I say err on the side of calling. Take a deep breath, keep a level head, stick to the facts, and answer the dispatcher's questions, and please, for the love of God don't start your call off with anything like "well I guess it's not really an emergency but..." that's basically our "it didn't scan, so it must be free" and don't apologize repeatedly for calling, if you feel bad about tying up an emergency line, all of that apologizing just makes the call longer which means you're just tying up the line even more.
The situation is different from one area to another, but overall a lot of places have moved to a sort of central dispatch model, more or less everything is going to go through the 911 center and very little gets dispatched from your local police station. In a lot of places, even if you call the non emergency number there's a good chance it's coming to us, and if it does go to someone at the station there's a good chance they're going to transfer you to us, or just take the information and call us after you hang up. In most cases I'd prefer you just called 911 and cut out the middle man, especially if you don't know exactly where you are so I at least have a landline address or cellular location to work with. The station can handle administrative things, getting a copy of a report you already filed, answering general questions, lost & found, etc. but if you need a cop to do something, even if it's just give you a phone call, that's probably going to come through us.
In your situation, I probably would have called when someone was banging on your door. That kind of tells me that the situation was out of hand and was potentially even presenting a threat to yourself. You seem to understand that as well since you went for your gun. If there's a situation where you think you may need to defend yourself and you have the time to do so, you should probably be calling 911.
I probably also would have called the front desk about the yelling. Cops may not care about your noise complaints, but the hotel probably has their own noise rules, and if the guests are breaking them, management can have them trespassed, and the cops will care a bit more about that.
Final thoughts, since I'm somewhat on the inside, I have a pretty good handle on the overall attitude of the cops in my county. Overall, I trust them not to show up and shoot someone having a psych episode, or be too unreasonably racist, or otherwise do something that's going to end up on the news in a bad way. Certain officers/departments I trust more than others, and I'd be more or less willing to call about minor issues based on that. In a situation where I don't know the local cops I'd err more on the side of not calling. My overall guidance of "if your not sure, call" still applies through.