@kallard - the best option is to use WiFi-C (WiFi Calling) if your phone is capable of that. The call quality and reliability is much better. AT&T, and us, will not be supporting the MicroCell forever so upgrading your phone would be best.
As far as the "best" MicroCell, the black DPH-154 is the newest model and probably the end of the line. It has a smaller footprint and newer radios, but they did away with the Computer port (which was useless and problematic) and the external antenna port. Otherwise, it's functionality (3G only) is the same as its predecessors. The downside of your model is the ac adapter. If you are using the original adapter that came with it they do fail after awhile causing all kinds of odd issues. See my Quick Tips (link is in my sig line).
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.