Shape and weight first
Specs matter less than how a mouse sits in your hand. Compare its length and width with your hand, and think about how you hold it: with your whole hand (palm grip), your fingertips (fingertip) or in between (claw). Light mice, around or under 60 grams, are popular for fast shooters. Heavier ergonomic mice with a thumb rest are comfortable for long working days.
Left-handed? Choose a symmetrical mouse, although many models only have side buttons on the left.
Sensor, DPI and polling rate
Every modern gaming mouse has a sensor more precise than your hand. DPI says how far the cursor moves per centimetre; most gamers play between 400 and 1600 DPI, so the maximum on the box is mostly marketing. The polling rate (for example 1000 Hz) is how often the mouse reports its position. Higher values are a touch smoother, but ask more of your processor and battery.
