Kakashi is the coolest so far because (and this is only for the anime viewers) we don't know his backstory and so he seems so much more mysterious. While Itachi is just a really self-obsessed butthole who has no allegiance to anything or anyone. I also feel that Kakashi's mellowness is totally better than Itachi's villain act. I just find laid back characters that much more bad-ass because I start imagining what it might be like if they tried hard or got infuriated.