Hi,
According to Wikipedia:
http://en.wikipedia.org/wiki/Advanced_S ... RadiometerASTER GDEM covers the entire earth at 30m resolution. The SRTM DEM covers the US at 30m, and most of the rest of the world at 90m resolution. So, there seems to be a huge advantage of ASTER data for non-US routes.
However, the NED 1/3 arc second DEM data has a resolution of 10m and, where available, 1/9 arc second NED even 3 meters! These are only available in the US though, 1/9 even there only in select places (check Western Maryland!) So, if you have ReDem, I think you should stick with it and use the NED data, it should give you MUCH better and 'crisper' elevation data, with a lot more detail on your "demed" terrain.
Cheers,
Michael