I don't favor require, I require it (sorry for the pun).
The main issue is that include() will just emit a warning and continue if the file doesn't exist, often leading to a confusing fatal error in a completely different part of the code; in other words, On Error Continue Next, PHP version. Even worse, people who use include are even more likely to use @include().
Oh, and require_once(), while we're on the subject: "if you're purposefully trying to require() a file twice, you're doing something Very Wrong."
The main issue is that include() will just emit a warning and continue if the file doesn't exist, often leading to a confusing fatal error in a completely different part of the code; in other words, On Error Continue Next, PHP version. Even worse, people who use include are even more likely to use @include().
Oh, and require_once(), while we're on the subject: "if you're purposefully trying to require() a file twice, you're doing something Very Wrong."