Most guys in MI waters will use the smaller scorpion stingers as mentioned above. I think their size resembles emerald shiners, which is the predominant forage for walleyes in that area once the mayflies are done.

Like others have said, you need to troll pretty fast for spoons to be effective. In most situations you want to pull them between 2-3 mph, which means summer water temps.

That said, we catch lots of walleyes pulling larger spoons in the Central basin while fishing for steelies. We get tons of walleyes of all sizes on the medium sized spoons in that region. However, the fish are likely chasing rainbow smelt in the central basin, so the size of the forage is different. In that section of the lake, we typically use 4-5 inch spoons.