I'll also throw my opinion behind Plex. I love version .9. The media manager stalls sometimes, but nothing major.
I have movies in iTunes, so I can stream to an AppleTV, but my AppleTV has the GPU issue (green screen), so I'm using Plex now, and couldn't be happier. I haven't looked much, but I wish I could just right to a list of TV shows from the main menu, instead of having to go one level down. Maybe there's a setting fot that *shrug*
In fact, I like it so much that I'm contemplating making it my full-time frontend. I have a TiVo as well, so files would be automatically pulled from the TiVo and re-encoded (with KMTTG), then added to Plex, so I have a single source for all my stuff. Currently, the sticking point is figuring out the season/episode number. The TiVo will give you episode #, but that doesn't translate right to season/episode. You can do a lookup on thetvdb.com to map them, but that's a bit of work. Maybe someone else has already done that. But I might script it. *shrug*