It's far from being my personal preference or decision, but more like the conclusion of a decade long debate and discussion of the pro gaming communites.
I'm buying gaming mice since they exists (last century), but the "fact-based" dive into the subject only started getting serious for me when Sujoy released his
mouse score in 2007. Since that day, I'm reading all(!) threads and post on esreality and
overclock.net (and on all the other related forums) about mice. I really like the subject just like how I read all the other hardware sites about GPUs or CPUs etc, or perhaps even more since I'm still an avid gamer and I love quality PC products.
If the mice has tracking issues, unwanted accel/deceleration at different movement speeds, if it jitters on certain surfaces or pads (etc, etc) those are all attributes which you might want to avoid when looking for a mouse.
I agree that those tiers on the picture are stupid (if not retarted), but it's still a good starting point for somebody who knows little about the subject. If you are also interested about my personal opinion, I do like angle snapping for example, and I find it funny that the guy put perfectly fine mice into shit tier just because of that, but I do accept that my opinion is the minority here, and I do accept that it's something which can be seen as a con or a flaw. We are all kinda purist here when it comes to computer hardware, that's what enthusiasm is about to pursue the best and the perfection in every detail.
Again, I did not state my personal preference, but the sum of the users of many gaming persons/communities. The G400 sensor is simply flawless at 400 and 800 dpi, (little jitter above on some rare surfaces, but 800 is more than enough for everything), so it's finally a perfectly tracking gamer mouse.
BUT, it has a cheaper lower quality submini HIMAKE wheel because it's more quiet. The build quality is also lower compared to the g500 or the MX518 and to the more expensive mice, the buttons are also little lower quality (even if they are D2FC-10 million click now on paper) and the stock teflon is too thin and wears of quickly on the front, so the bottom line is that if the high weight is not a problem for you (if you lift;D) than it's a perfect mouse tracking wise, but you might need to replace it in every 1-2 years if you use it a lot, so it's deserved to in on the top of the list.