Cork screws. Had loads of them and half of them have either broken or they're too stiff to work properly. Have tried the ones with the pull down wings and inevitably the cork gets stuck up the barrel never to be retrieved again, except with saintly patience and a pair of long-nosed pliers. Even tried that device with the compressed air widget and managed to coat everything in view a pale burgundy colour.
I've always wanted a really fine device like the sommeliers use and have eventually found one in an Italian market @ 2 Euros! Brilliantly simple and effective; a short, sharp blade for the foil, an easily deployable screw for inserting and a perfectly formed arm that rests against the lip of the bottle enabling perfect extraction every time ! Bliss.