Demons are a serious problem for the Winchesters throughout demons a little too well.
Some of these demons they even ended up allying with for various reasons. There is that saying that there's always a bigger fish, and it's true of Sam and Dean's world where monsters and gods exist. Since the demons in Supernatural can have complicated motivations and don't always act evil, take a look at some of the D&D Alignments of more notable demons.
Abaddon: Lawful Evil
Abaddon doesn't just respect order, she wanted to created one. After destroying the Men of Letters and time-jumping to the 2010's, she set out to reform hell into the terror that it once was. Her evil was generally strategic, like her collection of souls both from innocents and from crossroads deals to help power hell.
Even her possession of her vessel was a strategic move to infiltrate the Men of Letters. She didn't just destroy them immediately, but thought of her mission first and bided her time until the right moment.
Dagon: Chaotic Evil
Dagon is a prince of hell, one of the original demons that Lucifer created, so it's no surprise that she'd be incredibly cruel. But oddly enough she's introduced just in time to protect Kelly Kline and Lucifer's son.
It's not really for Kelly's benefit, though; Dagon flat-out tells her that she's going to die from birthing a nephilim, and that she's super pumped about Jack wrecking the world. It's debatable that she does it out of loyalty to Lucifer, because what she really wants out of the situation is more power.
Azazel: Lawful Evil
Azazel was a loyal follower of Lucifer. He performed a ritual killing multiple nuns so that he could communicate with Lucifer and help figure out how to free him from the cage. Everything he did to the Winchester family after that was in service to Lucifer, setting up the apocalypse.
He dealt with Mary to feed Sam demon blood, took John Winchester's soul hoping he would break the first seal, and set up the competition between Sam and the other special children. Azazel's evil was always calculated, and it was always for Lucifer.
Cain: Lawful Neutral
Cain was definitely evil before. But when he met Dean, he'd gone more into neutral territory. He sat out the squabbles of good and evil, refusing to participate on either side. He wasn't going around murdering people anymore, and was in fact making herculean efforts to abstain.
But he also wouldn't immediately help Dean with his quest, even allowing demons to beat the crap out of him in Cain's house. He later decided to kill all of his descendants, but it wasn't out of sheer evil; it's because of their potential for more evil.
Alastair: Neutral Evil
Alastair just loved being evil. That's to be expected from one of hell's master torturers. He could recite the prophecies the demons believe in, but he didn't seem to care about them aside from the fact he could torture Dean with them by letting him know how he started the apocalypse.
Instead of simply itting that the demons weren't killing angels, he let Dean torture him before finally telling Sam that the demons wouldn't just stop at a few angels if they were capable of killing angels. He wasn't chaotic, but he didn't work for a cause so much as a ion.
Lilith: Lawful Evil
Considering that Lilith was willing to sacrifice herself to free Lucifer, it's easy to see that she fought for a particular cause. She believed so strongly and was so loyal to Lucifer that she was willing to initiate an apocalypse she wouldn't even get to see.
She also seemed to value what hell does in its corruption of innocents; she preferred to choose children as meatsuits when she walked the earth. The use of children's bodies to torture those around them (and desire to eat babies) shows that she was pretty dedicated to corruption.
Asmodeus: Lawful Evil
Asmodeus was always loyal to Lucifer. He even tried to unearth the Shedim to please him. Too bad Lucifer didn't like him back. After this unrequited bromance, Asmodeus lay low for a long time before trying to claim the throne of hell.
Even then, he said he was basically holding it for Lucifer, and sent demons to check the cage for him. When that didn't work, he tried to get Lucifer's son on the throne (even though he wanted to be de facto regent). Granted he later turned on Lucifer, but Lucifer kind of earned it.
Ruby: Lawful Evil
Ruby has the distinction of being the one most dedicated to Lucifer's cause. She went through some truly crazy crap to seduce Sam to the dark side, even letting all the other demons but Lilith think that she'd betrayed them.
She worked on him for a couple years just to get him to free Lucifer, and even went so far as to feed him her own blood. She risked everything and was ultimately murdered for it anyway. She was also so good at her job she managed to break up Sam and Dean; that takes some carefully planned evil.
Crowley: Chaotic Neutral
Crowley has had a long and winding career in hell. He started as a salesman making deals for souls, but ended up the king. Then he somehow ended up dying for Sam and Dean Winchester of all people.
He proved himself probably the smartest demon on the show by not underestimating the Winchesters, and going the extra mile to protect himself from all manner of beings that were stronger than him, including Lucifer himself. But that's the real point about Crowley: for the vast majority of his time on the show, he was always looking after number one.
Meg: True Neutral
Meg was one of a few dark beings that ended up working with the Winchesters. For the first part of her time on the show, she would've fallen more into Lawful Evil. She was dedicated to the cause of Lucifer and the apocalypse. But when that fell through, she had to find something else to believe in.
She discusses the search for a cause with Dean at one point, and mostly ends up just looking after herself. But one can't stay completely evil hanging out with the Winchesters, so she moves more into neutral territory by the time she sacrifices herself to help them.