The G303 and G502 are the only mice on the market with the PMW3366 sensor.
The G302's AM010 is an old sensor with a pretty low malfunction speed. If you're a low DPI player and need to turn around fast, you MIGHT notice strange sensor behaviour. You basically can't make the PMW3366 malfunction like this. Not only that, but it is noticeably better than even the best implementation of the older PMW3310 that most pro players use in mice like Zowie FK/EC/ZA, SteelSeries Rival etc.
I've used the Mionix Avior 7000 with the 3310 for a year @ 800 DPI and yesterday I bought a G502. Wow, the sensor improvement is insane! Perhaps casual players wouldn't be able to tell, but as a point of reference, any Global Elite in CS:GO should easily be able to tell the difference.
I had to return the G502 though, it was way too big and heavy for my playstyle. But after using the PMW3366 sensor, there's no way I'm going back to a 3310. The G303 is the only choice for me right now, and the ambidextrous design should be perfect. I might dislike the fact that there's no rubber on the sides, but other than that I think this is the perfect mouse for first person shooters right now.
Also, Logitech mice have amazing click delay. Compared to other mice, you will get in far less situations where you're sure you shot that one guy with the sniper before he shot you. The G302 obviously also has this advantage over other brands and could be perfect if you're on a budget and just started playing a game like CS:GO.