i have tried all three of these amps, at different times...
i liked the distortion of the blackstar, but did not care for the clean side at all. the distortion kinda of sounded the same no matter what level of saturation was dialed in... in other words, it had one sonic fingerprint.
i liked the layout and sound of the H&K, and thought the touch sensibility of the 18 was really nice, but i found the distortion side of it very two dimensional..
this was the same effect i found from a similar model made by Egnator.
i found the boogie to be head and shoulders above both of these amps, both in quality of distortion, three dimensionality, flexibility of multiple sounds out of one amp (perfect for recording)
plus
the top boost setting (clean channel, top boost switch, 25 watt power amp setting, pull master on the CUT) was my favorite setting...
and the 15 watt class a setting on HI 2 for the classic boogie thing was sorta in the neighborhood of my old Mark 2b, but only sorta.
it's a good lead tone, that's for sure.
just MHO