I had a 2011 merc pro kicker. It was the loudest, most cold blooded animal I ever owned. I had a hell of a time trolling with it. It was constantly throttling up and down. I had it at the dealer a few times. I couldn't hear myself think when trolling either. Maybe I just got a bad motor. I know plenty of people happy with their mercs.
Last spring I bought a 2012 yami t9.9. Let me just tell you, ITS KILLER! The motor trolls so smooth and is so quiet. When its rough its hard for me to tell its even running. I have a throttle controller on it through my autopilot and it trolls down very nice. Starts right up. I wouldn't ever hang another kicker on my rig.
However, I have a mercury pro xs main motor and love it. The kicker just didn't do it for me.
Andy at shipyard island marina had the best price around. I bought it from him online. They tank test them before they ship the motor. I did all my own rigging. Andy was only a phone call away when I had some questions. http://www.shipyardisland.com