I think 2 hooks are better, especially for Coho;
I'm by no means an expert, but I find fish generally get hooked with the front hook, the back hook digs in somewhere else in the head.
I've actually turned to using a trailing 2/0 Treble hook with a sliding 4/0 Octopus loops leading. This way if a fish hits, it will corner the Sliding hook, and hook the trailing under the jaw, or in the gill plate, the two hooks pull towards each other, keeping the hooks in the fish... I do the same for Anchovies
Keep changing your leaders every couple of weeks, the drawback with this system is that if the rear hook goes, as they can after a bunch of fish, the front hook has nothing to pull against...
To get the sliding hook, simply put a loop of line through the O of the hook, and place around hook, if that makes sense.