Joey and Chandler (Friends) - It's somewhat down to the performance of Mathew Perry that this works on such an effective level. You can tell that despite being way more intelligent than Joey there is a genuine fondness that really shines through. Not to mention that Chandler pretty much supported Joey his whole adult life since his acting never brought in much cash. I think it was Chaos who said he was broken up when Chandler moved out for good and I definitely felt that too. In the last episode, their goodbye felt the most sincere.
JD and Turk (Scrubs) - These 2 remind me of how I am with my friends. Always starting stupid catchphrases, playing games and having a few beers whilst watching silly stuff on TV.
JD and Turk were the reason I made this thread. I was watching Scrubs last night and honestly couldn't think of better on-screen best friends than those two.
They are hilarious together, always have each other's back on the show and the way the two actors play off of each other, you'd think they had been best friends in real life for years. TONS of chemistry between those two.
Their bromance is one of my favorite things on TV.
Chandler and Joey is a great selection. You can also go with DJ and Kimmy from Full House, or Richie Cunningham and The Fonz from Happy Days. There's so many "best friends" in sitcoms that it's extremely hard to choose one of them.