God, this was posted five months ago and nobody has replied! So I will.
Kaoru is better because he's more mature and doesn't have anger management issues (no offense to Hikaru).
Hikaru is better because he's more evil(in a good way).

Kaoru is better because he's thoughtful, frequently painfully cute, and willing to sacrifice anything for Hikaru. I especially love him in volume 12 when he gets all worried that he's not going to lose Hikaru. The devotion is just lovely.

Hikaru is cool because he's so posessive and protective. I think it's just adorable~

to me hikaru has more of a holy shit side to him and kaoru has a oh crap side to him...........in other words....
Hikaru- anger management, caring, evil,and etc
Kaoru- sweet, caring, careful, and etc!!!

It's tough to pick who I think is better, because neither of them are. Hikaru is selfish, but he's honest and you would probably always know what upsets him.... where as Kaoru hides everything though he does it so he isn't a bother and in the way. Hikaru is devilish, where Kaoru is mischevious. It's tough to say who's better than who. They both complete each other, and yet each is really different. Each has flaws and perfections. :/

Hard to say Karou is better because he's more mature and kind. While Hikaru is more harsh and evil but in a good way

both are good at manipulating people to get them to do or say things.but,Karou follows Hikaru's plans more often then vice versa.Hikaru is emotional raw and doesn't know quite know how to express him self.Karou is softer,more controlled and expresses himself better.

they are the twins.neither of them can be better.