There are two small atlases I consider to be absolutely indispensable. Sky and Telescope's Pocket Sky Atlas is one of them. The charts in this atlas were well chosen. Each covers just the right amount of sky to give both a good perspective of the area you are looking at, and enough detail for star hopping with binoculars or finder scope, (stars are shown down to magnitude 7.6). Stick figures highlight the constellations to provide an easy and intuitive reference for what part of the sky the chart covers. An all sky view key of the charts is provided at the back of the book so that charts are easily located. The charts are well organized and very easy to navigate.
The charts are printed in color and are works of art in their own right. Not only is the atlas useful in the field, but it is a pleasure to browse through anytime.
The construction of the atlas is also very well done. It is spiral bound so that the charts open flat, making them easy to view. The charts are printed on good quality paper that looks as though it will stand up well even on nights when dew is challenging your ability to view.
Although it may seem like a small thing, a nice feature of the Atlas is a scale on the front cover from which one can construct a set of circles based on the field of view of each instrument you observe with. There is even a template showing the circles of a Telrad finder. It would have been even better if a clear plastic template with field of view circles had already been included, but it was easy enough to create my own set of circles.
Overall, this is an outstanding atlas for taking into the field, and I would certainly recommend it. As I said, I consider it to be indispensable; however, unlike others, I do not consider it to be the only quality pocket atlas out there. Another outstanding atlas is The Observer's Sky Atlas by E. Karkoschka. It is a nice compliment to Sky & Telescope's Pocket Sky Atlas. I like the Pocket Sky Atlas for its big broad views of the sky and it's stunning charts. I like the Observer's Sky Atlas because it has some additional detail (see my review of that book) not available in the Pocket Sky Atlas. Both are ideal as field atlases, and I keep them both very close at hand when I've observing.
I hope you're not in a position where you can only buy one. Choosing between the two would be difficult. As I said, I keep both with me when I'm observing. But if you do have to choose, I would suggest the following. If you want the nicest looking atlas, go with the Pocket Sky Atlas. If you want a bit more detail and you don't mind giving up the glossy color pages and spiral binding, go with the Observers's Sky Atlas. But honestly, you really can't go wrong with either one.