Your first decision is portable (ala Brake Buddy style) or fixed. If fixed, there is a further choice of those with removable brake piston (ala Brakemaster) or the "nothing to remove" types (M&G, Air Force One, etc.).
They all seem to work pretty well, so it may be just a matter of preference and your particular needs.
If you want a portable, Brake Buddy is still the gold standard - they've been doing it the longest and have an excellent track record. And their latest model is very convenient to use.
That said, I use a Roadmaster Brakemaster system, mostly because my coach came with the necessary air line already installed, so all I had to add was the car side of the system.
2004 American Tradition; 2013 Buick Verano
Homebase in the Ocala Nat'l Forest near Ocala, FL