I have to say, I favor Bert to Ernie, but love both of them. I tend to find Ernie loses a lot of his character's humor without BErt (or at least someone to annoy). There was a great Ernie and Grover opposites song they made recently (after Steve took on the role at least), that was just as funny.
Truth is, Bert isn't boring... he's overly exaggerated boring. Which means, of course, he's funny because he's so dull, everything is a characature. Not to mention, like most of Frank's characters, he can get some great improvised bits, and overexasperation...lik his constant fainting.
You look at Ernie's Show and Tell or skits where he sings with Elmo and you see him just being a kid. Not too much going on. You ad someone to annoy, you've got classic humor. In short, Bert could be kinda funny on his own, but Bert makes Ernie great.