Considering that the device has been around for three centuries, and has excited so much ingenuity and artistry that there are thousands of designs, there are a lot of bad corkscrews. Anyone who opens more than one or two bottles a year should invest in a proper one. There are two main aspects to the design.
First, the screw, the part that actually penetrates the cork, must be the right shape. Avoid those that look more like a gimlet or drill than a spiral. These will tend to drill a hole in the cork, and will not grip it. The result, on pulling, is a shower of cork dust with the cork still in the bottle, or broken in half. Look for a screw formed in a spiral, with an open centre. This will grip the cork properly. The tip should be sharp.
Second, consider the design of the pulling mechanism. The simplest sort, with a handle set T-shaped to the screw, leaves your arm and shoulder muscles to provide the pulling power, which is acceptable for the fit and strong — though even they will be defeated by very tight corks. Look for a corkscrew with a leverage action that braces the corkscrew against the neck of the bottle. The simplest sort is the "waiter's friend", which has a claw-shaped arm attached to one end of the handle. This is lodged against the bottle neck. This corkscrew is effective with practice, but be sure to buy one with a long enough, properly formed screw.
Another design of corkscrew is the butterfly, which has twin handles operating through a ratchet mechanism onto the screw shank to lever the cork out once the screw is inserted. The principle of these is excellent, but many unfortunately have the wrong sort of screw.
Counter-screw or double-action mechanism corkscrews are the easiest to use. A common design is the boxwood double-action, which has two handles, one of which drives the corkscrew, while the other rotates the wooden screw set around it to extract the cork. The outer body provides the locator for the wooden screw, and the handle for the user.
An advantage of this sort is that it is easy to position the screw over the centre of the cork. Metal variations of this basic design were common in the 19th century, and reproductions can be bought today. Some used a handle working through a bevelled gear onto the shaft.
The Screwpull is a modern design that is extremely easy and effective to use. It has a plastic body which rests on the neck of the bottle. The very long screw is wound down into the cork, and continued winding draws the cork out of the bottle almost effortlessly. The Screwpull has the added advantage of ensuring that the screw hits the centre of the cork. This device was designed by an American oil engineer, Herbert Alien, using the principles of oil drills. A luxury version has a handle to provide the leverage, bringing the cork out with one easy movement.
Avoid devices that pump air or gas into the bottle. Faulty bottles have been known to crack or explode under such treatment,