Trace vs polygon pour
The only reason this could be an issue is if your running logic or RF signals above 50 MHZ and are concerned about reflections. Reflections occur when you have sharp 90 degree corners in a trace or a plane. Cut corners at a 45 degree angle. If it is a trace the length of the angle is 1.618 times the trace width. For planes you can use a polygon pattern to break up standing waves. Remember that the copper is already there and you are paying to have it removed. Planes have a lower cost for that reason, plus the labor to run wide ground and power traces into tight places full of parts and vias. For best performance you should have software diagnostic tools to predict signal behavior before having the boards made.