Traffic volume influences what I choose. If traffic is congested for the most part I'm in the right lane. Because traffic is congested and not moving very well the merging causes less of an issue. If traffic is light and flowing pretty well I may choose the center lane to avoid the mergers, again this assumes traffic is light and I can maintain speed. I will not use the center lane if my speed is impeding traffic flow.
I try to pick a lane that allows me to flow with traffic while maintaining ample/increased stopping distance.
Traffic volume, road conditions and weather all impact what lane I am in. It's not as simple as right lane or center lane