I use both... each have advantages. Transcoding features can be tweaked on each so that is not really an issue, usability is however. TVersity is a must more for audio than video since it is nice to have podcast playlists and internet radio when you feel like listening to something different while playing.
For video TVersity is great for the same reasons (video Podcasts etc) but if you have a great deal of video (recorded TV episodes etc) on your networked PC then viewing it via the dashboard/TVersity is a real pain. Since the dashboard just gives you a long list of titles to scroll through I prefer to the Extender/Transcode360 so that I can see the files organized in folders. But then I seldom use the 360 for anything but HD Video since XBMC is much much much better than anything the 360 dashboard or extender is capable of in their current versions.