Rigging convention for limb joint dominant axis? Typically with bones you would use a dominant access for bending a limb (knee, elbow, finger etc).

When the roll is set you can choose to use the X or Z axis, (Y axis runs along the bones length).

Even though I realize you can use different rotation methods (Quaternion, Axis-Angle etc... which can be less restrictive compared to Euler rotation), its still convenient to have the manipulator aligned so an axis runs along the bones dominant axis for bending.

Is there a convention for rigging here? or does everyone choose differently?
In my rigs, the dominant rotation axis is always X.

It's consistent with Rigify's convention, and less a hassle when using X-Axis Mirror for faster alignment. Could be confusing, though, because visually it's always the Z axis that looks mirrored. So I'd just pay attention to the Z axis when orienting the bones.



For translation bones (like sliders) I use the Z axis, also because of the way X-Axis Mirror aligns symmetrical bone rolls. That is, if the animators use Gimbal transform orientation, they could focus on using the red (X axis) part of the rotation widget, and blue (Z axis) part of translation widget.