RR, I know of a couple big name guides in Oregon who both run Merc's but say they would run Yamaha's in a heartbeat if they were comparably priced and if there were as many Yamaha shops/mechanics as there are Merc.
I've run both for years in Ak. and if money wasn't an issue, I wouldn't even consider a Merc.
Yamaha is easily the outboard of choice among the Ketchikan and Craig charter fleets.