Le Lead is the destination of choice for modern high-gain tone.
Clean channel A offers quite a contrast compared with what channel B is capable of. By itself, it records well and can deliver a pretty cool boost pedal for an amp, but to a player looking for high-gain sounds, it may perhaps be of more use when used in the Fusion modes to blend with channel B for adding a touch of clarity to the compressed saturation or boosting it for extra gain.
Anyone looking for rock and metal tones to combine with a speaker simulator for a complete system might like to give this a listen: channel B's swept-mid EQ is able to variously set up scooped sounds or add boost for extra body or presence.
Like Le Crunch, though, when using the pedal purely as a dirt box, we find the gainier voicings bright and need to tame the fizz to get results that complement our amp.