Favorites:
1) Vergil 3 (DMC3) - He's not designed to be fair, he's designed to open up a can of vergil all over your ass, so prepare your anus. Even on normal difficulty this guy is a rape train, so beating him is a legit pulse pounding victory.
2) Nelo Angelo 1 (DMC) - something about making the most out of your limited kit makes beating him very satisfying. This boss was the first time in any game I was forced to learn a boss's patterns and tells, but once I did, I was reading entire combos from the vaguest of telegraphs and I felt like a motherfucking jedi.
3) Agni & Rudra (DMC3) - uncooperative camera aside, these two are really fun to style on with royal guard
4) Credo (DMC4) - This boss makes table hopper fun as ****.
5) Phantom (DMC) - just a really well rounded boss fight. The environment is cramped so you're forced to go toe-to-toe, you have a relatively safe way to deal damage if you're not the best but he's got a sweet spot that puts you in range of his stinger if you like high risk/high reward.
Least Favorites:
1) Savior (DMC4) - a glorified platforming puzzle, 90% jumping to new platforms, 10% fighting things. The beginning o the end for DMC boss designs
2) Sanctus 1 and 2 (DMC4) - vulnerable to taking damage, okay, let me just run away constantly until my shield comes back. Not hard, just really annoying, and beating him feels more like a chore than a victory
3) Vergil (DmC) - a sad shell of his DMC3 self, every attack is painfully telegraphed and deals pathetic damage, and the frequent cutscene interrupts are a really intrusive way to announce his insignificant pattern changes. He doesn't feel like a boss fight, he feels like a character begging for death, handing you the keys to his life bar on a glowing, grapple-indicating plate.
4) Geryon (DMC3) - stop your galloping bullshit you cheap piece of- MY WHOLE LIFEBAR?? I HATE YOU YOU ASSHOLE HORSE. Hate levels reduced once I accidentally discovered the sweet spot on his face that will stop his gallop and cause him to fall (for like 2 seconds) but still one of my least favorite fights
5) Dante (DMC4) - the DMC version of fighting dark link; every move you do has an instant counter hard coded into his AI. Beating him feels more like exploiting holes in his otherwise flawlessly cheap counter pattern than it does beating a boss. Also being on the other end of a just release is painful as hell