Cleaveland dies do very nicely
I have some old, non-springback dies I bought with a bunch of tools a while back. When tackling my RV project, I decided to purchase the Cleaveland dies.
Testing them side-by-side, I could see a definite difference in the quality of the Cleaveland dimples. In particular, they leave the area surrounding the dimple much flatter than the other dies. It is worth noting that a wimpy squeeze with the Cleaveland dies leaves a similar result to conventional dies, but if you seat the Cleaveland dies fully, the result is a beautiful, crisp dimple that fits the rivet perfectly and almost resembles a countersunk installation after driving the rivet.
I haven't tried the Avery springback dies, but have generally been happy with their products as well.
M