Mitchell's is one of my favorites. Some folks have trouble with it in hard water. My boar brush takes care of that issue.

I have a bunch of PAA, Asylum/Bullgoose, West Coast Shaving, Chiseled Face, (etc.) soaps, and they all lather excellently regardless of the brush.

Haslinger is one I use my boar brush on, but I'm not sure it needs it. It lathers very easily and has such a great post shave feel. I love the slickness during the shave as well.

I do use that technique where you lather the soap upside down initially. I let the first suds drip out. They are usually full of bubbles and aren't useful later into a shave. As you keep lathering the thicker suds gather on the brush, and you can add water from there as needed. There are very few soaps I've had trouble with using this method, even in hard water.