In reply to Roger Irrelevant:
the reduced distance you'll fall with a 12cm quickdraw vs. an 18cm quickdraw is almost totally negligable once you consider rope stretch and the slack in the system...
Personally I think 18cm draws are a nice length for trad. For sport I like to have a variety of lengths, but think it's more important to have stiff, preferably fatter tapes on them - mostly because if you pull the rope through, longer floppy quickdraws can flip round into a 'backclipped' position which sort of negates the point of leaving draws in if you are working something.
There's nothing quite like being mid crux and hearing 'you just backclipped...' from your belayer for blowing your redpoint.
Also if you are into working routes, the fat petzl express style tapes are much better for grabbing and yarding on than newer style skinny tapes.
What I did for a bit was got a set of shorter tapes for sport climbing, and longer floppy ones for trad climbing, which works ok if you don't do much of one discipline, but I got sick of having to swap them over and at some point got a second set of sport climbing quickdraws. I have four each of the 11cm, 17cm and 25cm lengths, and for what it's worth the 17cm usually tend to be the most useful.