I would have to say Troy Aikman. He's sharp, quick, generally spot on. He's clean, portrays himself well on & off camera. At times I think he allows his past professional ties to the Cowboys effect him. To the degree that it appears that he makes an extra effort to critique the Cowboys in general in a negative fashion just so he won't be considered a 'homer'. Perhaps it's just my Cowboy fandom kicking in. Having said that about him, I still don't see any other TV play by play broadcaster doing a better job.
Who you got?
Who you got?