There are always up and coming assistants and not many of them last as head coaches.
Well it's funny you say that, honz, because Phil Jackson, Gregg Popovich, and Jerry Sloan are examples of assistants who did last as head coaches. (BTW, Sloan is the only one who has been fired as a head coach. He was fired by the Bulls.)
If you are implying that it's better to go with an existing head coach (or former head coach) among the ones available, I'd say no thanks. Philadelphia can have Doug Collins. Avery Johnson, Jeff van Gundy, and the freshly fired Mike "I can't even coach a king" Brown have had their chances. It is unbelievable to me that Mark Jackson is even being considered for a head coaching job. (Rick Carlisle and Rick Adelman would have been worth considering, however, over the past couple of years.)
I'd generally go with an assistant over a college coach, too, because the success of college-to-NBA path is mixed. Popovich did coach at the college level, but he was an assistant--and GM--before becoming a head coach. Chuck Daly and Bill Fitch won titles, but that was 20+ years ago. Rick Pitino, John Calipari, Tim Floyd, P.J. Carlesimo, and Jerry Tarkanian all had underwhelming NBA head coach stints.
Thibodeau has years of experience, including assisting several NBA title teams. He has worked with foreigners. And he has been interviewing for years. There might be other options, but not many with his background. Utah's loyalty to Sloan is no less damaging than their loyalty to Kiri and Memo; the Jazz re-signed those guys without looking around. And Utah continues to fail to meet their potential. Utah was better than a 5th-seed team this year, and they were better than getting swept in the second round, even with the injuries.