I haven't tried nMage, but own the majority of the oMage line. If I were to start a game of Ascension, I would use the Revised rules with the Second Edition fluff. Revised attempted, for reasons that are unclear to me beyond someone saying "You're having badwrongfun!", to constrain the focus of the game to Earth by making travel to the spirit world difficult and, eventually, fatal. As many Reality Deviants mages escaped into the Umbra to escape the Technocratic calcification of reality, this was a substantial shift.
I, for one, loved the idea that there existed fully-explorable realms created by human belief, and that mages could find sufficiently sympathetic ones in which to set up shop. I enjoyed the idea that one side or another could still win the Ascension War. The post-Revised setting seemed to take all the cool, hopeful, and generally non-WoD elements of the game and smash them. This led to a game that felt to me to be counter to the spirit of the prior editions. While the mechanics were tightened up, I didn't think the tradeoff was equal.