I noticed that one of the 'benefits' of CamelCase was that it's easier (aka. faster) to type however I'm not convinced that's a benefit. In my mind, each line of code should involve spending some time thinking about its content and structure both as an individual line and within the context of the broader codebase. Underscores force you to slow down and consider your variables and to me that seems beneficial.
Maybe if you're hacking together some fast script that you want to rapidly test and debug then coding speed would be beneficial but I have always approached coding as a slower, more deliberate step-by-step process. This may however stem from my mainly doing code in Matlab, et. al. for computational analysis, where considering how the maths is performed is just as important as laying down variables.
(Disclaimer: Unless I'm doing a night-before homework assignment in uni, at which point my variable names become 'fuck', 'fuckfuck', 'fuckitall', etc.)