I dont truly have a favorite map that I enjoy playing over the rest. However, this railgun map is the best map I have seen for competition because of the moving train in it.
This causes the strats to be totally dynamic. Crossfires wont just be setup and wait for the enemy to appear and see who has best guns. For those of you new to the RTCW world, this is what RTCW has become. No more cookie cutter strats that everyone uses and tries to execute to perfection.
Most of the ET maps are setup with multiple objectives like this but this particular one has a variable path and the offensive and defensive setups vary depending on where the objective (the train) is. Some of you wont truly appreciate how this makes the map so dynamic but for someone who has spent hours upon hours settign up strats for RTCW only to be forced to resort to some old setup that everyone and their pet gerbil does, this is just refreshing. Fear my runon 
Ok, now that I have ranted and praised a bit, I suggest to the mappers planning on doing maps for this game work with this same idea. Doesnt have to be a train and it doesnt have to be something you ride. It just has to have an objective that moves and that the axis and allies can sorta control. Perhaps a key to start the launch code and the axis need to use it to set the right sequence while the allies have to turn off the sequence. Dunno, I have got too many ideas to do a bad job explaining them here. I just wanted to shed some light on why this map can be so fun and can last a long time and still feel fresh.