Boss HM-2 is a similar kind of distortion pedal as the Boss MT-2. Out of the two pedals the MT-2 does have the biggest range, because of the parametric EQ it will let you dial in almost any sound you want. The MT-2 also has more volume and gain compared to the HM-2. The HM-2 may sound more natural and organic to most ears. What about using the two together to create a unique distortion sound? The goal is to use the HM-2 and to tweak its sound with the MT-2, because of the wider range of the MT-2 and also because of the pedal having more gain.
Experiment with the placement of the HM-2: HM-2 after MT-2 may be best, but it is possible to do it the other way around as well.
Once you have both pedals in place, dial in the sound on the HM-2 to how you like it, tweak this sound with the MT-2. Try to create an almost similar sound from the MT-2. Once you have done this you will notice it will make the HM-2 sound fuller.
Next, go for a more extreme setting on the MT-2 to add more spice to the HM-2.
The bonus of using both pedals is being able to get feedback at will. Both pedals will work well with single coil pick-ups and humbuck pick-ups.
Each pedal used on their own may sound dryer, once you use both pedals at the same time your sound will be wetter, fuller and having more sustain.
You may like the idea of using both pedals at the same time for a section of a song, or you may like to play an entire song with just the sound of both pedals. Whatever you will try, you cannot really go wrong with any of them.
Happing playing and hope to see you soon again,