Race-style bike repair stands
If you've a particularly delicate fleet of bicycles (think high end carbon or ultra-thin steel) then this will likely be the system for you. They are usually come in a little higher in the price range but also tend to offer more features. Most importantly, given that they operate by cradling the bottom bracket and clamping the forks at the dropouts they don't put any unwanted stresses on your seatpost or any of the frame tubes themselves.
Many offer the ability to spin on a central axis, meaning you can access the whole bike without really having to move yourself. Naturally to make the most of this you'll need to keep the stand in a relatively central location, making them more suitable for larger workshops and commercial shop floors.
One thing to note is that if you're blessed with a variety of bikes you will need to make sure all your axle standards are accommodated, and given that mountain bike wheelbases have been getting stratospheric in recent years, that it's long enough to fit your off road machine comfortably.
Clamp-style bike repair stands
More common and usually cheaper, these are often a riders first point of entry into a life of constant bicycle maintenance.
One thing that cannot be stressed enough is that wherever possible you should always clamp to the seatpost, rather than the frame itself. You really want to avoid any accidentally dented or cracked tubing. If you do have to clamp the frame, do so gently, and pad the jaws with a rag or some old inner tubes to reduce the forces and increase grip.
If you've got a wide range of bikes to work on this system is probably a better option for you, given that the clamp is universal. Also given that wall-mounted options are available, if you're operating in a confined space then this may save you some valuable real estate.