Nuke has kind of become the vfx darling, or 'flavor of the week' over the past few years. Both nuke and flame are very capable, very powerful products though.
Incidentally, since we're talking autodesk, I am partially responsible for their newly launched knowledge base site: http://knowledge.autodesk.com/ 
My primary (visible) contribution was building the custom faceted search that kind of drives the whole site.
