MM is the best. Not sure why CSI seems to get the nod in public opinion.
Here is my comparison is anyone cares:
Price, selection, packaging, shipping speed, and free shipping threshold: Both excellent.
What MM does better:
Quality of games offered as daily deals, ability to stack multiple daily deals on the same order.What CSI does better:
White Dragon Enterprises
seems to have the best regular prices and the same free shipping threshold. They don't have a daily deal per se, but a lot of great prices via auction lately.