I'm a bit hesistant about rechargeable AA these days - some of them are a bit oversize and can get stuck in battery slots that are 'close tolerance'.
Conversely, I really like AA powered lights, especially for more than just commuting. Because if my batteries and my spare batteries die and I'm in the middle of nowhere, I can spend a small fortune on a pack of AA at a garage somewhere.
USB rechargable lights are great for commuting if you work in an office where you can plug them in when you get to work etc... But not everyone does, I used to work in a brewery, unless I could plug my light in to a 3 phase 32A socket, there was no way I could charge it... Hence AA's.
J