Everyone's ears are different but to my ears, there's no comparison. The Rebel is just a much, much better amp. Comparing the two side by side, which I've pretty much done, its a laughable difference. You'd be kicking yourself for a long time if you take an ht over a Rebel. Maybe not but probably
I went from a HT50 to a Rebel 20 and its the best amp I have ever owned. It is so responsive and feels so alive in comparison to the HT50. Ive had a lot too - Orange TT, JCM 800, DSL50, Bugera 1990, Laney LC15, Jet City JCA50H. The Rebel suits me down to the ground, and our other guitarist with a Tubemeister has tone envy... i have skill envy mind you...
edit: having said that I probably wouldnt attempt dream theatre or maiden on it... im a sure an OD could help, but it shines in the lower gain classic rock territory for me.