Mice
There are many aspects to gaming mice that arn't advertised, the market is very anti-consumer, pushing high DPI mice that perform poorly compared to their older counterparts.
DPI:
The amount of pixels your cursor will move per inch you move the mouse. Contrary to popular belief higher dpi does not result in “more accuracy”. Most competitive players use between 400-1800dpi. High DPI mice are generally worse because they have smoothing to comepensate for their outrageous claims, Zowie is one of very few examples of mouse manufacturers who make mice properly without this marketing charade.
Jitter:
Jitter is unpredictable involentary mouse movement caused by the sensor misreading the surface below it. At lower DPI this issue shouldn't really exist. Mice with high advertised DPI that don't appear to jitter on higher DPIs are almost garenteed to have smoothing, this usually carrys across all DPI settings, degrading the experience for people who look past it.
Smoothing:
Smoothing is the process or reducing jitter via post processing, it can give a feeling of input lag and unresponsiveness. It is generally used on mice with stupidly high max DPI’s to make it stop jitter at DPIs that the sensor can't properly handle (It's a marketing ploy which degrades the quality of mouse even at low DPI).
Polling Rate:
The amount of times per second your mouse scans for movement. This ranges from 125,250,500 and 1000hz. Higher polling rate is generally better but there are odd occasions where it may be better to use 500 instead of 1000hz (Mice with smoothing may feel more responsive, such as the Mionix Avior 7000).
Malfunction Speed:
The speed at which your mouse will stop responding in a predictable fashion. It’s rated in meters per second, e.g my mouse it rated for 7 m/s. Low sensitivity players generally want this to be in excess of 4m/s to avoid issues with fast mouse swipes.
Sensor:
Optical is pretty much the definative way to go, they normally offer a slightly lower DPI than laser but are less prone to jitter and don't have random acceleration like laser mice. The Steelseries Xai and Logitech G9X are examples of popular laser mice but they generally only liked for their shape and design.
Friction:
This is an issue that isn’t really talked about but can and will effect your gameplay. The texture of your mouse feet changes as you use them which will change the amount of friction you are provided with, higher friction is useful for people with less accurate fine movement or a higher sensitivity but it will also slow you down. Tighter weaves tend to polish mouse feet which makes them glide slower over time so bare that in mind.
Weight:
The weight of your mouse also greatly affects your gameplay, a lighter mouse will be easier to start moving and will have less innertia than a heavy mice. Generally speaking lighter mice are better for lower DPI and heavy mice are better suited to higher DPI though hand size and personal perference all play a role.
Considerations when buying a gaming mouse:
What sensor does it have?
What is the malfunction speed? (Higher is catigorically better if it isn't achieved though software trickery)
What firmware does it have? (Did the manufacuture bork the mouse by forcing it to have a higher DPI than the sensor supports?)
Will it jitter on my mouse pad? (Tight weave pads like the Puretrak Talent can cause issues)
How heavy is it? (80-90 Grams is about the sweet spot)
How big are the mouse feet? (Large mouse feet provide more friction but last longer)
For the sake of the arguement let's compare logitech's "flagship" mouse with one designed by quake players.
Ninox Aurora:
Shape: Flat sides so you don't have a grip type forced upon you.
Max DPI: 4000.
Weight: 70g (unspecified if that's with or without cable).
Price: £34.46 (Including delivery).
http://ninox.org/products/mice/aurora/
Logitech G502:
Shape: Looks like something from Bad Dragon.
Max DPI: 12,000 DPI (Yeah, we even use commas now).
Weight: 168 grams (with cable).
Weight: 121 grams (without).
Amusingly enough it has a weight system incase you want to require the use of a pulley system to operate it.
Price: £55.51 (Currently reduced from £70, I wonder why).
http://gaming.logitech.com/en-gb/product/g502-proteus-core-tunable-gaming-mouse
I'm aware it's not fair to compare an "ergonomic" mouse with an ambextirous one but it just goes to show the difference between what the corporations want to sell us and what we actually want/need.
I even did a survey on what informed gamers actually want from a mouse (click here).