Over the last little while I have noticed some talk here and there, on why Maya does not have a simple tool for rounding or creating a circle from an edge loop selection as other applications do. Enter the sort_Cirlce_tool, a script written by 9box on creative crash, the Sort Circle Tool for Maya will create a perfect circle shape from a selection of two boarder edges.
sort_circle_tool will create circle shapes from an edge loop selection in Maya
Providing an interface with aligning options, methods for selections, and an axis for aligning the circle edge loop, the sort_circle_tool makes super-short work of moving edges and verts around in a round circle. Simply call the sort circle tool for the user interface, and the sort circle script for the main procedure.
It is important to note, that the selected edges do need to be boarder edges, or from a hole, or the outside edge of a shape working equally. Check out the sort circle tool for Maya here.