how to choose a _____

if you have questions tweet me: @tiburonCS

== how to choose a: gaming mouse ==

you should rule out:
any mouse that doesn't fit your hand
any mouse with a bad sensor (laser sensor or bad optical sensor)
any mouse from a sketchy manufacturer (google "[name of mouse] overclock.net" for reviews+feedback).

hand size is the most important factor in choosing a mouse.
measure length (from wrist crease to tip of middle finger) and width (across your palm, index to pinky knuckle). you can use these measurements to compare with folks online. I have very small hands (7.75" length) so I know my options are strictly small mice like the G100s or Kinzu. I can rule out anything designed for normal/larger hands.
shape and weight also go along with this. your preferred shape will depend on how you like to grip your mouse. weight is preference. if you can go to a shop and hold a bunch of different mice, that will give you an idea of what you like.

once you have a list of mice that will work for your hand, prioritize in this order:
1) sensor quality/performance. Obviously, you don't want any hardware acceleration (so only optical mice allowed, no laser mice). You also don't want any input smoothing or angle-snapping built into the mouse. do you need a 'perfect sensor'? I would actually argue that you don't necessarily. people on overclock.net like to freak out about the minute differences between 2 sensors and which one is more 'perfect'. But ultimately, you may have to make some compromise between the shape/size mouse you want, and the sensor performance of the mouse. So while you may not have the 'perfect' sensor, you still want as good a sensor as possible.  Above a certain threshold, many different sensors will be 'good enough'. GuardiaN (top 3 CSGO player in the world) has godly AWP aim with a Kinzu v1, commonly considered to have a trash sensor.
Currently the 'Top of the line' sensors are the Avago 3310 and 3360.
sensor also includes 'swiping' features -- aka Lift Off Distance and Perfect Control Speed. A faster perfect control speed is always good, while LOD is preference.
2) features/build quality. what texture mouse? do you want braided cable or rubber? adjustable weight? macros? wide range of CPI settings? do you absolutely need side buttons? do you prefer light clicks or more tactile clicks? do you want a bunch of stupid lights on it? also obviously you want a mouse that won't break after a month.

anything that's a preference will take experience to know which you prefer. once you find a mouse that fits perfectly, has the features you want and good sensor -- stick to it! the more you know about your own preferences, the easier it will be to find a new mouse if the old one breaks.