A single hander for coho is better because you should always strip in as much line as you can. Coho will follow it right in. Its a pain to get the shooting head back out of the guides say on a spey rod compared to two false casts on a single hand. Coho respond much better to stripped flies. They also hangout in spots that are conducive to cast and strip, not swinging. But for Chum and Chinook, a heavy spey is what you want ideally.
For coho, comets, clousers, woolley buggers (heavier hook than trout buggers), egg sucking leech etc. Chinook and Chum will take anything from #10 comets to the biggest intruder you got. Chartreuse works like magic on fresh fish. Have a good selection of popsicle type flies for swinging. Colours combos like black and red (for low and clear), blue and chartreuse, pink and purple, black and purple (coloured water) etc.
When fall rolls around and its choked with fish, FISH LIGHT TIPS. This avoids fowl hooking fish, and trust me it happens.