In general the higher the flap setting the quicker you get off the rwy but the worse your climb performance.
Hence flap 18 will give the highest t/o speed but the best climb performance whereas flap 30 will get you off the rwy quicker but will impare your climb schedule. So short field t/o will require a higher flap setting.
We have no performance for a flap 33 t/o hence we can't use it. However we are shortly going to be approved for flapless take offs (on ferry flights only)
As for Co SOP's we are free to use whatever setting we see appropriate, except for the obvious senarios
Noise sensitive t/o = flap 18
Contaminated rwy = flap 30.
As for LCY we usually use flap 24 however if your heavy then flap 30. Although with a 100 series flap 18 works very nicely.
[ 18 July 2001: Message edited by: notac ]