I'll give the exact same ranking of those 3 fanbases as you. Giants most tolerable, Steelers the absolute worst, and Cowboys in between. However, maybe just by total coincidence, the vast majority of Cowboys fans I actually know personally are really nice and good sports. Here's how I profile each fanbase.

Giants fans - Obnoxious, but if I'm being honest, we'd be just as obnoxious if we had 2 SB wins against the Pats in the last decade too.

Cowboys fans - Surprisingly respectful and not sore losers (or even excessively dickish in victory) in real life (as opposed to the internet). That said, they are total bandwagoners who only acknowledge the existence of football for as long as the Cowboys remain contenders. Additionally, they are painfully stupid football fans. At this point I've just programmed myself to talk to Cowboys fans the same way I talk to my 90 year old grandmother about football. Seriously, they don't know shit about the game.

Steelers fans - Corpulent, inbred, cretins. These vile monsters can be found polluting the otherwise majestic landscape of Pennsylvania anywhere west of Lancaster. Spend more than 5 minutes with one of these depraved imbeciles and you're likely to hear some of the most absurd and horrendous football commentary ever uttered, as well as a racist comment and a suggestion of a visit to the nearest fast food establishment. Unfortunately, because of the Steelers storied history and Pittsburgh's general appeal to the simpleminded among us, Steeler fans are a large tribe, and one cannot traverse the glorious state of PA for long without encountering one. The good news? Diabetes should take care of the vast majority of this plague in due time.