Niners yes, Titans no.
Also, Denver contends with Manning at quarterback. Strong o-line, good young receivers, weak (sorta) division.
Obviously, all that also applies to the Niners, who also have a better defense and coach. Not to mention an even weaker division. I honestly think he chose an AFC team because he still thinks a Manning-bowl is possible in the future. Maybe he doesn't like the weather in San Fran. Maybe it's because of Elway. Beats me, since I think the Niners definitely gave him the best chance to win.