forr... I think they are all good... and this board has strong supporters of each brand.
I have the E Brake by Jacobs(Cummins brake), and I love it. Towing like you do, it will be very nice. I use mine all the time, towing or not.
I have seen the pacbrake for about 550, e brake for 550, and not sure about BD or US Gear. The last time I researched them, I believe the BD had the best braking.
Any way you go, I would recommend the shifter switch from BD or a similar switch. I installed one and wonder why it took me so long to do it!