I'd recommend upgrading to either the MX500 or the MX510 for gaming, since the MX300 doesn't have the extra thumb buttons that come in super handy in most games, plus the shape is a bit nicer fit in the hand (assuming you're right handed). The MX700 is a great mouse as well, since it has all the features of the MX500 but is cordless as well, but some people find it a bit laggier than the corded mice in gaming. I've never personally noticed any lag except when the batteries were low, though.
I've never liked the MS mice. To me they feel cheap compared to the logitech mice, especially the left and right click buttons (way too mushy feeling). Also the scroll wheels on the Logitech mice turn in increments instead of turning smoothly like the MS mice, so they are better for selecting weapons in FPS games.