"According to Which Broomstick, the Firebolt's going to be the broom of choice for the national teams at this year's World Championship."
-- Lee Jordan (PA13)
Which Broomstick is a wizarding magazine which contains articles comparing the various types of brooms available, new brooms and other features.
There is an order form at the back that can be used to order a new broom (PA12).
In the UK, "Which?" magazine publishes special edition consumer guides such as Which Car and Which Laptop. Which Broomstick would fit right into this stable.
From the Web
WizardingWorld.com (Pottermore) features:
Harry Potter Wiki: Brooms