Both warriors were inconsistent and usually equal in terms of capabilities. But on an overall performance. Karna scores higher!
Points for my reasoning.
- Karna might have slightly more defeats, but he also had far more victories.
- He conquered the whole world, which is specifically mentioned in BORI CE as well.
- He also defeated the entire might of the Bharatha Kings in the Kalinga swayambara. Thousands of kings from all over the world were casually defeated.
- Ashvathma arguably performed better than Karna in Virata war. But at the end of the day, they both lost the overall battle.
- Other than that, we don’t see Ashthama in a lot of action. He mostly remains neutral. So it’s hard to gauge his power before the Kurukshetra war.
Now in Kurukshetra war. There was one day where Ashvathma completely dominated the battle. On the 15th day.
Pandavas including Arjuna were dominated by Drona’s son, who remained unvanquished in battle.
But karna dominated both the 16th and the 17th day, as well as the 14th night.
- On the 16th day of the battle.
He possibly defeated Arjuna and the other Pandavas once and then he defeated them again infront of Arjuna while simultaneously fighting him.
Having severed Hardikya’s bow and standard and killed his horses, he cut down Duhshasana’s supreme bow and attacked Radheya. At this, Karna abandoned Satyaki and struck Arjuna with three arrows. He then pierced Krishna with twenty arrows and struck Partha with three more. However, Satyaki advanced against Karna and pierced him with sharp arrows, first with ninety-nine fierce arrows and yet again with one hundred. All the foremost among the Pandus oppressed Karna—Yudhamanyu, Shikhandi, Droupadi’s sons, the Prabhadrakas, Uttamouja, Yuyutsu, the twins and Parshata.
The Chedis, Karushas, Matsyas, Kekayas and their armies, the powerful Chekitana and Dharmaraja, excellent in his vows—these rathas, horses, elephants and foot soldiers who were fierce in their valour—surrounded Karna in that battle and released many kinds of weapons. All of them devoted themselves to killing Karna and addressed him in fierce and eloquent words. Karna used his sharp arrows to cut down those numerous showers of weapons. He destroyed all of them, like a wind breaks down trees. One saw Karna angrily use his storm of arrows to destroy rathas, elephants and their riders, horses and their riders. The Pandu forces were slaughtered by Karna’s energy. Most of them lost their weapons and their bodies were wounded. They retreated.
Source- karna Parva critical edition of Mahabharata.
He was the only one who was stated to be capable of countering Ghatotkacha in a night battle.
Granted Ashvathma did great against Ghatotkacha and defeated him, but Karna thrashed Ghatotkacha and defeated him several times. Caught his Rudra vajra with bare hands.
He aka defeated every single Pandava Maharatha and could have easily killed Yuddhistira and ended the war on the 17th day.
- He has also made Arjuna retreat from the battlefield. Something Ashvathma hasn't been able to do.
‘ “At this, Kunti’s son, Dhananjaya, spoke to Vasudeva. ‘Behold the extremely terrible bhargava weapon. O Krishna! O mighty-armed one! Behold the valour of the bhargava weapon.
There is no means of countering that weapon in a battle. O Krishna! Behold the angry son of a suta in the great battle. The brave one is like Yama and has performed a terrible deed. He is repeatedly casting extremely terrible glances towards me. I do not see any means of running away from Karna in this battle. If a man remains alive in a battle, there may be victory, or there may be defeat.
O Hrishikesha! For the sake of victory, how can one be victorious if one is dead?’ O venerable one! Janardana wished to leave to see Yudhishthira and thought that Karna would be overcome with exhaustion in the battle.
Karna Parva critical edition of Mahabharata.
As for Astras. Both were master of all the Brahma weapons. Both possessed the Brahmashira weapon, so that point is mute.
Ashvathma had the edge with his Narayana weapon, but it can only be used once and it can be countered if a warrior simply surrenders.
But even if all of this is ignored, there’s a direct answer on why Ashvathama despite having immense potential never managed to achieve many great feats. It’s his lack of control.
He used a supreme weapon in battle like Narayana astra in battle, infact he dared to use another supreme weapon aka the Brahmashira missile on pregnant women.
Warriors like Karna and Arjuna did use astras on warriors in battle. Arjuna previously used the Vajra on soldiers, Karna used the Brahmastra. But they still never used it on innocent people, only in war and out of desperation.
Karna while brash, kept his weapons under control and steadied his mind. Which is what allowed him to counter all of Arjuna's weapons in his final battle.
He performed so well thT even Shree Krishna offered his sudarshana chakra to Arjuna after looking at Karna's performance.
Near the end of the battle. Arjuna's weapons were exhausted in battle and he was afflicted by Karna's weapons.
If Ashvathma learned to control himself, then he probably would have been better than both Arjuna and Karna. But this brash behaviour led to his downgrade.
Ashvathma started out better but Karna eventually surpassed him. The feats clearly reflect the overall growth.
Hence Karna proved himself to be the better warrior. Over time Karna learned to be better, and by the end ofwhile Ashvathama did not.