The best, aside from price. - Geissele Super Charging Handle

This is the best AR charging handle I have ever encountered, smooth as glass whether you run it on either side by pinching it thumb-pointer or conventionally by hooking pointer and middle. It also strikes an impressive balance between aggressiveness in design and texture for getting ahold of it and not being so aggressive as to stab you to death slung up. It is a fair bit more pokey than the stocker, but all of the other benefits make that a worthwhile trade off. Also it has gas-in-your-eye mitigation designed into it, another benefit over the stocker.