Loweflyer,
At this time, I think most would agree that the SkyRadar L-Model is the cleanest and most practical ADS-B receiver. You probably need to determine what functions you are looking for from an ADS-B device first. There really is not "Best Choice" unit as each has its own uniqueness. Below is a basic rundown.
iFly 700 / 720 - Weather only (SkyRadar Newer L-Model)
iFly 700 / 720 - Weather and ADS-B Traffic (NavWorx ADS-600 or SkyRadar S2 & D2)
iFly 720 - Weather, Traffic and AHRS (iLevil, shipping next month) May possibly support the 700 via wired. We are waiting on the development device to confirm.
If you looking for a IN/OUT ADS-B Transciever, look at the ADS-600B.
New up and coming ADS-B receivers for the 720 and wi-fi... iLevil, Clarity, FreeFlight are being developed with the iFly. This ADS-B market is evolving and moving very quickly. This information is changing each month as more units are being released. I really the new iLevil shipping this month or next. I hope this helps.