Hi Bob,

I have been flying with WxWorx weather for about 18 months and I have been
extremely pleased with the service and the NEXRAD refresh rate. The primary
limitation to the XM service is the absence of coverage outside of the lower
48 (unofficially, XM reports coverage throughout much of Mexico, the
Caribbean and parts of Alaska). There are a number of portable solutions
available as well as panel mount options. I use the Garmin GDL69A satellite
receiver and display the weather on a Garmin MX20. The MX20 is a little
slow, but has proven more reliable than my previous PDA-based system.

ADS-B has a lot of promise, but has the disadvantage of limited service
volume (unless you are in the northeast) and is a ground-based transmission
system, so you may not have reception until you are airborne. Here in the
Rockies, IF we had coverage, it would likely be unavailable over most of the
mountainous portions of the state below 14,000'.

I'm afraid I'm not that familiar with the WSI vs. XM debate.

Here is a link to the WxWorx web site:
http://www.wxworx.com/aviation/receivers.php

Best Regards,
Mike