Quick Draws and Karabiners
Quickdraws are generally available in several lengths, and also with a choice of solid gate or wiregate karabiners.
Lengths: The longer and floppier your quickdraw, the less likely twists and turns in the rope are is to lift your gear out of position. So for trad climbing, a selection of quickdraws from 15 to 20cm long, plus one or two of 30cm for deeply recessed placements, is ideal. Consider too carrying 60cm (and even 120cm) slings equipped with two krabs apiece for use under roofs etc.
For sports climbs and walls though there is no chance of the bolt lifting out (at least one hopes not!), so short 10cm quickdraws are fine, and are easier to clip, especially if the lower krab is held firmly in place.
When using quickdraws, the idea is that the tightly held krab is the one that you clip the rope into so that should always be on the bottom end of the quickdraw. This is particularly important when bolt-clipping as falling off on bolts can put little nicks in the top krab. If this krab is then used at the bottom end it can put little nicks in the rope!