Given the potential weight on a Viking I'd go hydraulic. I'd suggest front only for the hydraulics and use the rear as a parking brake only with a mechanical calliper operated by a friction shifter. I have an Avid Code 4 pot caliper on a 203mm rotor on an ebike and it's simply awesome though not cheap. I got mine second hand at £35 which I thought was a bargain.
As per Danny's choice Clark always get well reviewed for their price and are a great choice one price point up from the bottom level. They generally perform well above what their price would suggest. If money is no issue then Hope mono but before you injure yourself laughing at the price remember I said no issue.
It depends where you are using your trike. Hydraulic brakes are softer on the hands, thus producing more pad pressure with less effort. On the other hand, they are impossible to fix in the field and quite expensive and labour intensive to service. I have switched to TRP Spikes on our new, heavily laden touring bikes. They have been superb with ample stopping capacity and I can adjust them, replace cables etc when I am more than 500km from a bike shop as now (western Queensland).