Sensei > Deathadder > G9x
It's very nice but the middle click really sucks hard. If you don't care about that, give it a shot. I don't really mind using any of the three otherwise.
There's no way I will buy a Sensei until they have a complete fix for the positive acceleration issue. I know some people say they don't see a tracking problem, but if there's any significant positive acceleration that can't be turned off, I won't buy it. So, that's why I bought a Deathadder and won't consider any SteelSeries mice right now (the same as many others feel). I'm not saying that no one should use the Sensei, but I personally won't because of that.