Bakugo wins this. Not only that he is very offensive and doesn´t have any problems to attack his opponent directly, he also outclasses Megumin in all terms (The only term which is maybe debatable is AP, but not only Megumin has to cast that spell first, she also can use it only one time each day and will knocked out because her low stamina/mana). Bakugo can blitz her before she can even react, and her durability might be only a bit above the regular human level.
Yeah, Bakugo wins this with probably zero diff, even if i really would give Megumin the win. Speed is one of the biggest disadvantages in Konosuba, and i don´t remember someone close to even Bakugo at this point.