Beagle, just one word of caution if you decide to invest heavily in any of these systems. Apparently most, or all, of these programs out there used DAFIF, a freely accessible US military database, as the source of their aeronautical data.
DAFIF is now gone. See an explanation on
http://www.navaid.com/dafif.html. All of these projects, therefore, now need to find new sources of aeronautical data, and some are more successful than others. If you need a solution right now, try to figure out where your program of choice is getting its data from, how accurate it is and how they plan to maintain that source in the future. If you don't need it right now, this might be a good time to wait and see what happens. Because there is going to be an inevitable shakeout in this area as all of a sudden the cost involved in obtaining the aero data (both financially and timewise) has gone up significantly.
PocketFMS, as an example, is transitioning from DAFIF to UMN, User Maintained NavData, where the users of PocketFMS themselves supply the aeronautical data, probably based on local AIPs, local charts and so forth. Apart from accuracy and timeliness issues, there's also the issue of legality and possibly copyright as well. It's going to be interesting to see how this is going to work in the next few years.
(Note that this is not relevant for anything that's based on the Jeppesen database. But as far as I know, these are very expensive.)
Regardless of what you use for actual navigation, make sure you have a legal, paper-based backup plan!