I love Jimmy. It's too late for Conan to come back, he's already made his home on TBS, and I hope it works out well for him. He's my favorite late night host. Jimmy Fallon is pretty funny, though. He's a nice guy, young enough to appeal to the pop/media generation, and he's relatable. Also, he's rather adorable.
Now, Craig Ferguson is a really funny guy, but I think moving him to something like the Tonight Show would destroy what he has, just like I believe it damaged Conan to some degree. Like Conan, Craig Ferguson is at his best when he's playing it to the hilt.
As for Jay, while I still dislike what he did and how he did it, I hold no ill will towards him. Both he and David Letterman will be put out to pasture soon enough, so I figure if you like them, enjoy them while they're here.
I think Jimmy will be a fine replacement. I just hope The Roots make the move with him, because those guys are awesome.
I tried to make a deal with the Devil, once. Turns out I didn't have anything he wanted.
You will never find a more welcome hive of love and humility.