in general oem is of better quality steel such as the marbane that gravely, JD and scag uses. The fusions are OK but it is only in the cutting edge. After a few sharpening's you can wear through the fusion into the standard steel and they also ding up easier than marbane blades.
For aftermarket blades I like stens and oregon for the price compared to most oem blades.
2013 Gravely 460Z 29EFI
2011 Gravely 36GR
2008 Gravely 160Z
2004 Gravely 34Z
1998 Lazer Z HP 48 (old faithful)