What do you prefer?
I'm not a huge fan of US sitcoms, but when I was young I used to enjoy watching Taxi. I was never hugely into Cheers until the last couple of years, but I really like it now.
I bought the first two series of Cheers recently on DVD and have enjoyed them no end. I recently got hold of the first couple of episodes of Taxi and did not think that the writing or the plots were anywhere near as strong as Cheers. At some points I found that the Taxi plots/dialogue were teetering on the edge of soppyness. That said, I still laugh at Taxi a lot and like the characters (Although Tony Danza's acting is slightly suspect), but ultimately Cheers is my favourite US buddy sitcom.