How To Pick A Mouse
Mice are primarily two things, Shape first and Sensor second. You could have the best sensor in the world but if you're hand isn't comfortable you're going to say that mouse sucks. I would recommend reading a more in depth guide after this and watching RocketJumpNinja as he does reviews as a gamer and gives feedback on the stuff that's actually important. Also I will never support Logitech or Razer mice. In my opinion, they are the "Turtle Beach" of "gaming mice".
A note for DPI. Ignore it. Also you probably shouldn't go over 800 DPI anyway. Less than 1% of "professional" gamers use 1600. The higher the DPI the more inconsistencies will occur, you can read more here. While we're talking about it, don't move the windows mouse speed from notch 6 of 11 on the slider. If you would like to know why, click here.
Aside from shape and sensor there is a variety of other factors to consider.
Button Switch Type like high quality Omron Switches.
Software Support for dpi, macros, or any at all.
Side Button Options. Usually mice have two, ambidextrous, or a full panel.
Product Warranty & Reputable Brand. I've had my Cooler Master Spawn since 2011 with CorePad mouse feet, it's flawless. I've had Logitech mice die, called them and read off the serial number, and they've sent me a new mouse free no questions asked, no return of the broken one.
Aside from some oddball mice there is a few standard shapes for the top mice. The following examples are where the original shapes came from and where the trends started.
Really only two choices have fully passed everyone's tests 100% of the time. The Avago ADNS-3090 & The Pixart PMW-3360. There is a running list on overclock.net showcasing mice with 3090's and 3360's. The 3360 list will continue to grow as it's the current king. If you're on a budget, grabbing a solid 3090 mouse is an acceptable option.
Mouse pad surfaces are the other half of the equation. They range from High friction(slower) to Low friction(slick). It's just a personal preference.
High Friction Pads
Lower Thread Count
More Resistance To Aid Control
Low Friction Pads
Mouse Feet (skatez)
And yes a lot of mice come with inferior mouse feet or slow feet. You can upgrade mouse feet from three companies, CorePad, Hyperglide, & Hyperslides. If your mouse isn't listed they can actually make them for you or send you the material to make your own. Keep in mind that by upgrading your feet the mouse will almost always move "slicker" or faster.
Mouse Grips (tape