I'm pretty skeptical Myers can bring it nightly. I know he's head writer at SNL, but SNL is kind hit or miss now, and he is only on screen about 10 minutes a week. Transitioning to carrying a show for an hour a night is going to be a big change. Fallon was the news guy too before Late Night, but he also was a regular performer in skits on SNL and is known for his impersonations and such. Myers has never been a big skit performer on SNL. He will have Lorne Michaels backing him so he'll have a long rope, but it wouldn't shock me if he doesn't last more than a few years.
Fallon right now for me is the funniest nightly show, but I fear he'll do like Conan when he goes to the Tonight Show. He already has been putting in some new skits that are Leno-like and they've bombed. I just hope
I'm seriously glad Leno is leaving for good this time (hopefully), and Letterman needs to follow suit. I tried watching Letterman a few nights ago and it was so boring. I assume they'll give the Late Show to Ferguson, which he's funny but he grates on me sometimes, and he relies too much on the stupid robot. Conan is still ok to me, but he's definitely not as good as he was back on Late Night.
Kimmel I haven't really watched enough to judge, but the few times I've seen he was funnier than Leno and Letterman.