Some say slow, some say fast, some say steady, some say lots of pauses. I say mix it up until you find out what works.
Common sense suggests imitating an injured baitfish; trollers report getting more hits when they turn or zig-zag, which will alter direction and speed of the lure.
Are fish up top, or hugging the bottom? Who knows for sure? I'd love to cruise the rivermouths with a fish finder and try to get a handle on exactly what the fish are doing.
Tons of theories out there, lots of internet experts, very little hard data. The guys that actually do the catching are actually out there doing the catching, not blabbing their sekrets on the interwebs.