Believe it or not, we actually covered the topic of capital letters in URLs and how Google treats them before. But the question was asked again and John Mueller of Google answered it in a fun way.
He said, "the use of caps in URLs generally doesn't help our algorithms determine the emotion conveyed on the pages."
Normally when people use CAPS in their communication, it is either (a) they want to be loud or (b) they have no idea how to turn off the caps lock.
Google doesn't know that you want to be loud when you use caps in your URLs. In fact, I believe Google recommends lowercase URLs because case technically can make for a different URL.
But overall, lower case or upper case, it is all the same. When it comes to URLs, I'd stick to lower case but it won't hurt you either way.
Forum discussion at Twitter.