Selecting the appropriate Windows Powered device depends on the work you want to accomplish and how you intend on using the device. Inbox works fine for reading e-mail and for writing short replies. And the new Pocket Word and Excel applications let you view and edit documents. However, external keyboards are becoming available to make this easier. The larger color screens are also much better for browsing the Web.
Color displays are better for visibility, but they also decrease battery life.
Whether or not you need this extra power and sophistication depends on how you intend to use it. This means you can store more data internally on them. The amount of time of continuous use with a fully-charged battery varies greatly, depending on the applications you use. Playing graphics-intensive games and listening to MP3 music drains the batteries quickly. The smallest is the HP Jornada 690, which is small enough to fit in a coat pocket.