Start with the codes you need to read. If you sell marked goods you need a 2D scanner that reads DataMatrix reliably, and a 2D scanner is also needed for QR codes shown on phone screens.
Then look at customer flow. In busy supermarkets a presentation scanner is faster: the cashier just passes the item in front of the window. Small shops and bulky goods suit a handheld scanner, and a wireless model lets staff scan heavy items away from the till.
Also check how it connects to your POS software (USB, keyboard emulation or COM), how rugged the housing is and the warranty terms. BDB specialists will recommend a model for your shop.