Sure, they both are evil tyrants hellbent on enslaving all the known universe, but Lord Boros was actually a pretty chill dude. He never fought someone weaker than him for shits and giggles. Hell in fact he came to Earth because of the prophecy that there would be someone there that could challenge him.

So yeah, Boros is evil, but he wasn't an asshole.

@NegativeSoul:
Upon arrival his spaceship leveled a whole city. He didn't care for his crew during the fight with Saitama and he was willing to destroy the population of a planet just for one good fight.
So yes, Boros was an evil, self-centered asshole. But he wasn't a sadist and he had some honorable traits, unlike Frieza.