USB rechargeable is the only way I'll even consider a light.
No, they don't hold a charge as long as a paid of AA batteries. But so what?
For my riding my big cygolites last for a couple weeks of commuting between charges. My smaller cygolites last about 1 week between charging. They give a warning that they are low when you turn them off (rapid flashing) so I get to work, charge them on my desk, and they are full again when I ride home. Easy as can be.
The larger cygolites (150 red in the back, 460 white up front) won't last more than 10 hours of constant use, but so what? Even if I rode 10 hours a day, there is a charger at my house when I get home.
I also don't leave them constant on. I have them blink at the lowest frequency. I find that's more than adequate for making sure cars see me and it makes the battery last much longer.