Although i also haven't looked into the latest version of Irrlicht i also would favour Ogre over Irrlicht as a 3d engine. Like AdrianT pointed out Irrlicht can turn into a mess. My problem with Flow, beside of that it's not in a finished state yet, is that it's not developed with the primary focus on it, it's more a sideproduct. I've already experienced how similar products went into a deadend situation and this is something i try to avoid whenever it's possible. Same goes with Max3D if Mark decides to concentrate on making games instead.