With purple skin marking him an outcast among his kind, Thanos is both burdened and blessed by the Deviant gene. At the same time, Hela is no slouch — she brought about her own existence by tricking Loki into creating her based on an alternative version of her that later grows up to become her.
It's complicated. The outcome of the battle between this pair of Universal Threats is also uncertain. Both of them are gifted in their own ways, and the magnitude of their evil deeds are likely equal. In truth, however, there will be a clear-cut victor.
10 Brute Strength: Thanos
Thanos' capacity for inflicting and receiving damage is almost infinite (having been greatly boosted after his reincarnation). There are several examples that prove this, such was when he casually knocks out an enraged Hulk and defeats the Silver Surfer with little to no effort.
But most of all, he manages to trap Thor in a stasis field, while the latter was augmented by the Power Stone on his helmet. Hela is also ridiculously strong, able to match Thor in a physical battle, albeit without the Infinity-enhancement.
9 Magic: Hela
Hela is a Goddess, which gives her access to all forms of Asgardian magic. She can create energy blasts that can kill Gods, travel across space and time, and also survive in her astral form due to her physiological resistance to damage.
One of her strongest attacks, known as the "Hand of Glory," is capable to stripping the flesh off the bones of even divine immortals. Thanos is also somewhat adept at magic, what with his jilted-lover cursing strategies, but they are unlikely to work on Hela.
8 Intelligence: Thanos
Hela is far from being stupid, given how she plots and re-plots her incessant attempts to seize the Asgardian throne. However, her intellectual talents cannot hold a candle to Thanos' ultra-convoluted, and somehow always successful, plans.
He is aware of all the latest developments in science, engineering, and technology, coming up with unforeseen solutions to them half the time. Thanos is rather arrogant when it comes to his own intelligence, stating that Bruce Banner is only smart if one considers humanity as a reference.
7 Force Of Will: Hela
Considering Hela's origin story, it is not unexpected that she has a far stronger will-power than Thanos (even considering his innate need to end half of all life). In the Final Gauntlet series, Hela falls in love with Thanos, and decides to bring him back to life after Gamora kills him.
This act is performed even though Thanos overtly rejects her interest, because Hela cares more about him being alive than the universe's joy at his death. Fortunately, the process is interrupted, resulting in Thanos coming back with a "broken mind," and both of them exiting unceremoniously through a black hole.
6 Invulnerability: Thanos
As a consequence of Lady Death's post-resurrection blessing, Thanos is now almost unbreakable. He can tank energy bursts that have the capacity to decimate entire worlds, even from beings like Galactus, Black Bolt, and Odin.
As a minor achievement, but still rather impressive, Thanos takes Wolverine deep inside his chest and grins like a maniac. Hela's durability, though incredible, can only handle relatively smaller attacks (such as bullets and Mjolnir).
5 Being Death: Hela
As the embodiment of Death in Asgard, Hela has some pretty explosive powers. As mentioned earlier, she half-succeeds in giving life back to Thanos. She can also literally kill someone by touching them (with or without her gloves on).
The really scary thing about Hela is that her powers of death are reserved for immortal beings, not humans and other entities who fall under a different purview. It remains a surprise why Thanos didn't fall for this version of Death.
4 Combat: Thanos
Hela displays a high degree of skill in combat, especially when armed with her Nightsword (she fought the likes of Pluto to a draw). Still, Thanos takes this round due to his prodigious talent for the martial arts, having been further instructed in warfare while living on Titan.
He can also use cosmic energy to drive his own metabolism — in other words, he fights till the other person flees or drops dead. Not even the Silver Surfer, backed up by Mjolnir, could handle Thanos in a direct battle.
3 Speed: Tie
Both characters have the ability to instantly teleport themselves, making the question of speed a moot point. While Hela's teleportation is linked to her magic, being a Goddess and all, Thanos' is more scientific.
His special chair is powered by something known as techno-mysticism, meaning he can telepathically connect himself with the chair. On doing so, Thanos can make it do various things, including transport himself to any location of his choice (even inter-dimensionally).
2 Equipment: Thanos
Although the comic arcs went through considerable alteration in the film versions of the Infinity Gauntlet story, the end result is the same. Thanos has all six Stones, and thereby controls the entire universe.
Nobody stands a chance against him with this piece of paraphernalia, not even Hela. In fact, the only useful item available to her is her cloak, which doesn't reinforce her powers as much as simply keeps her from not collapsing into a pathetic half-dead heap.
1 Winner: Thanos
This was not an even battle from the start. Thanos could effortlessly crush Hela, with or without the Infinity Gauntlet. The Nova Corps refers to him as a "Category 1 Life Ender," a mark that holds true considering he actually did go through with his life-ending plans.
Terrified of his dark intentions, the Shi'ar imprisoned him in the strongest cell they have, which he inevitably escapes from. There is no stopping Thanos. There is no beating Thanos. There is only Thanos. *snap*