>>302576'Straight gate' refers to a karabiner with a, er, straight gate. This is opposed to a 'bent gate' krab which is for the rope end of a quickdraw (usually only for sport climbing though).
If you know you need a locking one (screwgate), your next consideration is the overall shape of the krab. If it's for climbing and you don't have any already, you will want one that is suitable for belaying to start with. These tend to be more pear shaped, known as 'HMS'-shaped e.g. a DMM Boa or DMM Aero. These give a larger area for your rope and belay device to sit in that is well away from the gate.
DMM Boas are extremely versatile - later on in your climbing career you will be able to get 2 clove hitches into them, and they are dead easy to use with cold hands.
If you are only going to be climbing indoors, then a krab that prevents crossloading (the krab spinnng) is useful, such as the DMM Belay Master.
