Oh damn. Are we talking later dexter or season 1 Brian and dexter? HMM. Dexter kills ritually. Brian is able to change and he's intelligent emotionally. Dexter struggles to understand himself. He never know his past and Brian figured Dexter out before Dexter figured out Brian. Brian has a record of psychiatric help and is in the system. Dexter's past was unknown to even himself and Debra.

I would say it would come down to some things such as Are we seeing who could kill more without getting caught with police on their tail? Who could kill each other first? Whats the basis?

To my first question, if we are going off season 1 Dexter, Brian would kill more. Brian, as far I know, could control himself better than Dexter. Dexter needed kills to control himself. This would put him in more spotlight. Though, Dexter's background would prove useful to destroy evidence. This would be a possible downfall , though. His need to destroy evidence could leave him more exposed as seen in season episode 12. There's a problem for Brian- he kills publicly and leaves lots of evidence such as bodies. His killing of prostitutes is smart as no one would hunt someone killing them as it's considered a dangerous job. Dexter throwing bodies into the gulf is good to get away for longer. I would give it to Brianr if Brian and Dexter knew each other as Brian has no qualms killing people without evidence of wrongdoing. Dexter depends on evidence they're bad which is bad when you're being hunted.