Most of those places mentioned are pretty far out. For convenience to downtown with good access to training routes I recommend Alexandria, where I live. For better cycling routes but not quite as convenient to downtown, I recommend Takoma Park. Both have quaint "downtown" areas. Takoma Park has the edge for cycling routes. One good thing about Alexandria is that its a good launch pad to drive out west towards the Shenandoahs. Driving from Takoma Park adds a good half hour to that.