RTW has excellent mods... but if you do go with RTW I would recommend that you do not start with a mod. Play vanilla for a while (a few campaigns at least), and then start transitioning to mods when you start to get tired of vanilla. This way you get a basic grasp of the game mechanics first... most of the major mods are geared towards players who are already familiar with vanilla, so they can be intimidating and overwhelming if you just start with a mod.