Selecting the right Carabiner
When purchasing a carabiner the first question to ask is: what is it for? Are you going to be using it for belaying, anchoring, or racking your trad gear on it? This will help you to decide what shape is appropriate, when to use a wiregate or standard gate, and if you need a locking carabiner or a non-locker.

Some things to keep in mind when buying new carabiners:

• When you are climbing in cold conditions such as ice or alpine climbing, wire gates prevent freezing up better than solid gates.
• The only time you may use a bent gate carabiner should be on the rope side of a quickdraw, otherwise you will use a straight or wiregate.
• Size is also another factor. For instance, if you have small hands you may find that smaller carabiners are going to be easier for you to grip and use. If you are going to be wearing gloves it may be best if you choose larger carabiners with a big gate opening.

Full Article