Rather than write all that much about them, I'll direct you to Mark Evanier's website here, since he has a very nice and full write-up on Bob and the team.
I semi-sort of crossed paths with Bob Elliott once. The Museum of Broadcasting was having a tribute event to the team, which I went to. Bob was there, and Ray was supposed to be, as well, but he wasn't doing well and had to cancel. (Not all that long after, he passed away.) I almost never raise my hand to ask questions at events like this, and even more rarely get called on. But as soon as they asked for questions from the audience, I shot my hand up first, and did get called on. What I wanted to know is why the team ended up with the name "Bob and Ray," and not "Ray and Bob." Bob actually thought for a bit and laughed and said, "Y'know, that's the first time I've ever been asked that." He said he didn't have an exact answer, but back in the beginning their first radio show was called, Start Your Day with Bob and Ray -- because it rhymed.
Actually, I just now remembered mid-typing that about a year-and-a-half ago I wrote a fairly detailed article on this website about Bob and Ray -- where I told that above story -- and you can read the full article here. In fact, if you want to read even more about Bob and Ray (a LOT more...), the reason I wrote the article was to discuss a very enjoyable biography of the team, Bob and Ray: Keener Than Most Persons written by Emmy-winning TV comedy writer David Pollock, (the writing partner of my friend Elias Davis). If you'd like to track down the book, you can get it here.
It's not possible to pick a favorite sketch, or even really a Top 10. But let's just say this is one of my very favorites, among many. It's the "Slow Talkers of America."