The shuttlecock (or "birdie", if you're feeling casual) is the most fragile piece of equipment in any racket sport — a good one might survive a single hard-fought rally before its feathers give out. Here is everything I've learned about them the expensive way.
Feather vs synthetic
Feather shuttles are made from real goose feathers set into a cork base and are what every serious club and tournament plays with. They fly truer and feel better off the racket, but they're fragile and pricey by the tube. Synthetic (nylon) shuttles trade a little bit of flight authenticity for durability — a nylon shuttle can survive weeks of casual hitting that would destroy a feather one in a night. If you're just starting out, or your court is an outdoor one, start with synthetic.
Speed ratings
Shuttles are graded by speed, usually 75, 76, or 77 (sometimes marked slow/medium/fast). The right speed depends on the air: hotter, denser air at altitude or in a warm hall needs a slower shuttle, cold air needs a faster one. Most indoor stadiums at sea level in Canberra's climate sit comfortably around 76 for most of the year, but clubs will happily tell you what they stock.
Looking after them
Feather shuttles are happiest stored somewhere with a bit of humidity — a bone-dry cupboard makes the feathers brittle and prone to snapping early. Some players keep a spare tube in a humidor-style tub with a damp sponge; most of us just don't leave them next to the heater and call it a day.