Too me Ch4 is also great for more vintage/blues rock with the gain knob set fairly low. With the gain set somewhat higher it is of course a great heavy rock rhythm channel. I also use it as a solo channel for hard rock/metal (but ch3 is fantastic both as a rhythm and lead channel in that context as well of course).
Ch1 is great as a basic clean handling various colouring options.
IMO, Ch2 alone isn't my cup of tea, but it is really great with a boost in front of it, that's the secret of Ch2