Before even analysing the feats : my heart and guts say Snape stomps (no I have no bias ^^).
But in an actual battle I think Bella and Snape are close and I think this fight is the most discussed fight in HP.
Bella feats :
Duels : Bella has a lot of feats duelling people and often winning duels she is in.
Bella vs Kingsley : She beat him
There was a loud bang and a yell from behind the dais. Harry saw Kingsley, yelling in pain, hit the ground. Bellatrix Lestrange turned tail and ran as Dumbledore whipped around. He aimed a spell at her but she deflected it. She was halfway up the steps now —
Bella vs Tonks : She beat her
They both ducked again. A jet of green light had narrowly missed Sirius; across the room Harry saw Tonks fall from halfway up the stone steps, her limp form toppling from stone seat to stone seat, and Bellatrix, triumphant, running back toward the fray.
Bella vs Hermione Ginny and Luna : She stalemated the 3 and without her original wand
Bellatrix was still fighting too, fifty yards away from Voldemort, and like her master she dueled three at once: Hermione, Ginny, and Luna, all battling their hardest, but Bellatrix was equal to them, and Harry’s attention was diverted as a Killing Curse shot so close to Ginny that she missed death by an inch —
Bella vs 4 snatchers and Greyback
There was a bang and a flash of red light: Harry knew that the Snatcher had been Stunned. There was a roar of anger from his fellows: Scabior drew his wand. “What d’you think you’re playing at, woman?” “Stupefy!” she screamed. “Stupefy!” They were no match for her, even though there were four of them against one of her: She was a witch, as Harry knew, with prodigious skill and no conscience. They fell where they stood, all except Greyback, who had been forced into a kneeling position, his arms outstretched. Out of the corners of his eyes Harry saw Bellatrix bearing down upon the werewolf, the sword of Gryffindor gripped tightly in her hand, her face waxen.
Bella vs Sirius : pushed toward the Veil
Only one couple were still battling, apparently unaware of the new arrival. Harry saw Sirius duck Bellatrix’s jet of red light: He was laughing at her. “Come on, you can do better than that!” he yelled, his voice echoing around the cavernous room. The second jet of light hit him squarely on the chest. The laughter had not quite died from his face, but his eyes widened in shock.
So yeah Bella is quite the deadly witch and she is really really strong. That Molly the cake maker managed to beat her is quite the bullshit.
And Bella has numerous feats. More feats than Snape.
Bella magic prowess :
The Dumbledore blocking spell feat :
There was a loud bang and a yell from behind the dais. Harry saw Kingsley, yelling in pain, hit the ground. Bellatrix Lestrange turned tail and ran as Dumbledore whipped around. He aimed a spell at her but she deflected it. She was halfway up the steps now —
She was a very deadly witch and she was taught personally by Voldy himself. The most important and relevant Death eater in his army except the other player here.
She knows occlumency.
Bella portrayal :
She was always the closest to Voldy. The most loyal (with Barty JR).
Killed Sirius and Doby.
Among the Death eater she was quite respected. When someone met her they didn't brag.
She manhandled Greyback and the guy didn't retaliate. He must feared her (and she stomped him).
Bella was the only one who said aloud that she didn't believe Snape.
Snape feats :
Duels : here are Snape duelling feats
Snape vs McGo and after Flitwick and Sprout :
Professor McGonagall moved faster than Harry could have believed: Her wand slashed through the air and for a split second Harry thought that Snape must crumple, unconscious, but the swiftness of his Shield Charm was such that McGonagall was thrown off balance. She brandished her wand at a torch on the wall and it flew out of its bracket: Harry, about to curse Snape, was forced to pull Luna out of the way of the descending flames, which became a ring of fire that filled the corridor and flew like a lasso at Snape — Then it was no longer fire, but a great black serpent that McGonagall blasted to smoke, which re-formed and solidified in seconds to become a swarm of pursuing daggers: Snape avoided them only by forcing the suit of armor in front of him, and with echoing clangs the daggers sank, one after another, into its breast — “Minerva!” said a squeaky voice, and looking behind him, still shielding Luna from flying spells, Harry saw Professors Flitwick and Sprout sprinting up the corridor toward them in their night- clothes, with the enormous Professor Slughorn panting along at the rear. “No!” squealed Flitwick, raising his wand. “You’ll do no more murder at Hogwarts!” Flitwick’s spell hit the suit of armor behind which Snape had taken shelter: With a clatter it came to life. Snape struggled free of the crushing arms and sent it flying back toward his attackers: Harry and Luna had to dive sideways to avoid it as it smashed into the wall and shattered. When Harry looked up again, Snape was in full flight, McGonagall, Flitwick, and Sprout all thundering after him: He hurtled through a classroom door and, moments later, he heard McGonagall cry, “Coward! COWARD!”
Snape vs Harry book 6 :
Sorry don't find the quote but Snape stomped Harry badly. Harry mental state was all over the place and Snape mastery was just too much.
Snape magic prowess :
Here Snape shines quite a lot. The guy is a genius at magic.
Snape was also taught personally by Voldy. He managed to learn how to fly without a broom. Nobody can do it except Voldy.
The best occlumens in the whole show.
Creating deadly and powerful spells when a teen. Feat that barely know one of his gen did. (maybe creating the marauders map is equal).
Said by Sirius to have known even at school more than anyone about Dark arts. Likely his knowledge has increased since. Became teacher in DADA. Even Harry who hated Snape was amazed by Snape knowledge.
Can perform light magic too. He is the only death eater that can make a Patronus.
So he is an expert of Dark Magic and also how to fight it. He managed to fight back Voldy curse on Dumby hands (a great feat) for exemple. He also saved Katie Bell, fighting the dark curse of the necklace. Snape also created counter curse to his own dark spells sectumsempra.
The god king of potions.
Don't remember where but I think Snape also did one or two times wandless magic.
So clearly Snape is a genius in a lot of magic fields. And ones that can help in a fight : expert in dark and light magic, curse and counter curse etc. Creating spells no one knows too can help. And the guy can fly.
Snape portrayal :
Snape has also some portrayal inside the Death Eater : he was the one appointed as Headmaster. Voldy loved Hogwarts a LOT, and he choose Snape as Headmaster. And except the Ministry Hogwarts is the most important place in Great Britain.
I know that Bella likely didn't want at all the job, but Voldy put Snape as headmaster and this means that he valued his skills and granted him great status.
There is also a good moment at the astronomy tower : Bella, Greyback, Alecto, Amycus and Yaxley were there before Dumby and when Snape arrived everyone (but Bella) stepped back.
Snape was the only one who talked back to Bella and mocked her.
Bella and Snape were the two Death Eater Harry hated the most.
Conclusion :
Minerva was likely the strongest duellist both fought but Bella had a lot more feats duelling wise and good ones. Snape has likely more knowledge about magic in general and fighting magic. And Snape portrayal is quite good, even if Bella's one too.
Snape wins this but they are really close.
Tags for thoses maybe interested :
@Zoro D Goat
@Chrono
@Buusatan94
@AL sama
@IceWitch
@Dragomir
@MasterD