The first thing you need to consider when shopping for a keyboard case is whether it is compatible with your iPad. The first generation iPad and the iPad 2 have different dimensions, and many cases are built with one of those form factors in mind. Most cases won't fit both models, although some will.
Consider what size you want the keyboard case to be. The majority of cases don't add much size or bulk to the iPad, but there are size variations among models. Some of the very compact, lightweight cases have less typing room because the keyboards are very compact and small. Meanwhile, the heavier cases add protection, but can be so heavy that you might lose the portability advantage over your laptop [source: Stein]. Extremely light cases can sometimes slide down and not hold the iPad sturdily, especially if you have it in your lap, or on an uneven surface like a bed or couch [source: Patel].
The purpose of any case, keyboard included or not, is to protect your electronic device from the sharp edges, hard surfaces and dangerous liquids of the outside world. So, pay attention to the design of iPad cases when making a choice. Some models stay light by leaving large portions of the iPad exposed. That may not be ideal if you want more heavy-duty protection. There's also versatility to consider. Some cases use a prop stand to hold up the iPad (usually the leather models). Others have a solid hinged panel attached to the keyboard, similar to a normal laptop. Models with prop stands don't provide as many viewing angles as you might like, especially when you're adjusting the screen to get the best vantage point for movies or TV. On the other hand, the leather prop models can be easily folded back on themselves to make handheld use easier. Not all of the hinged models can do that.
The most important feature of any keyboard case is the keyboard itself. The keyboard designs vary widely. Since typing is a matter of personal preference and comfort, think about what you want out of a keyboard in terms of size, arrangement and the feel of the key presses [source: Sheehan]. In any keyboard case, the keys will be slightly closer together, since the cases are almost always around the same width of the iPad. Some cases make small alterations to keyboard layout that might be a deal breaker for finicky typers, like removing the right Shift key, or shrinking down the spacebar.
Many keyboards are made of a continuous rubber sheet, with no spaces between the keys. On the plus side, these reduce the weight of the case, and make them spill-resistant. On the down side, they don't have that familiar clicking noise, and the key presses can be more subtle, leaving you second-guessing whether you hit the right key [source: Patel]. Keyboard cases with separate keys may be the only choice for some. They still won't have as much clickety-clacking as a normal keyboard, but they can provide a more laptop-like experience.