Nice dilemma to have! LV has so many lines; the MC is one of my least favorites. I think Chanel is more subtle and luxe looking. But as others have said, try to get to stores where you can try both on and then decide. I have the GST and it's a good bag for me, 'cause I carry a lot and I'm a shoulder bag girl. Some think it's too boxy, but for me it's fine. The caviar leather is really sturdy. The cerf I'm not as familiar with. You may fall in love with LV MC. Unfortunately, it's one of the most faked of the LV designs, so that may be something to consider.
Good luck!