Depends on the driver. If there is not much window for driver breathing in the basket of the driver, then I prefer a 1/2" R cove bit. If the magnet gets in the way of breathing in a thicker baffle, then maybe a cove plus 45* chamfer to finish it off.
For some drivers a 3/4" roundover is enough, and 8" drivers are more typically don't require the relief.
This is a 1/2" cove followed by 45* chamfer, and the driver was a 4.5" with very little basket breathing room:
This is a 1.5" baffle combined with limited breathing room. I used a 1/2" cove, then flush trimmed to the cove relief, and then rounded over the inner edge with a 3/4" radius.
This is just a cove bit between the screw-mounts as it's traditionally done:
Hope that hekps,