I've never been able to stay awake for much late-night TV, certainly not every night, but I prefer Johnny Carson to Leno, Letterman to Leno, and Conan to Leno. Leno does have the honor of succeeding Johnny Carson, but that almost went, and should have gone, to Letterman. Meanwhile, when he succeeded Letterman, Conan was known as a writer, but I'd seen next-to-nothing of his onscreen persona. I came to enjoy his intellectual brand of humor, a hunor that doesn't seem as mean-spirited as Leno's or Letterman's. I thought Conan was doing fine on The Tonight Show and he would build a following just as he did for Late Night.
But the conflict between him and Leno is less about comedy than it is about Leno deciding years in advance to retire and then changing his mind, very reminiscent of the Brett Favre-Aaron Rodgers succession with the Green Bay Packers. When Green Bay finally cut ties with Favre, he struck deals with the Jets and Vikings, displacing the development of their young quarterbacks.
If life or business were fair, NBC wouldn't allow Leno back to The Tonight Show. He somehow convinced NBC he would succeed with a 10 PM show. The rest of NBC's schedule is in such tatters that execs at the time decided to give up dramas at 10 and install Leno, an unmitigated failure (see Favre with the Jets).
Sure, Conan could have a show elsewhere, but it won't be The Tonight Show, just as The Late Show isn't The Tonight Show, the show Letterman and Conan paid their dues to host.
UPDATE (01/19/10): Here's Leno's perspective. As MysterLynch wrote in the Comments, Jay says NBC forced him to retire last year. I apologize for assuming Leno was trying to hang on at any cost.