I have not found my pis to be slow and they usually sport libraries up in the hundreds of films and TV shows.
Still if you are using a PS3 with all it does (which is not an awful lot) you might consider a roku box, possibly with some hacks. In the UK they have also been sold under the "nowTV" brand and you can stick a version of plex on there which is going to go toe to toe with most of that.
http://www.automatedhome.co.uk/av-d...inute-hack-10-wireless-plex-media-player.html
If you have the right home network and the inclination then you will not beat the price there.
If you only care about streaming xvid and scene style H264 around your home network (or from a powered hard drive) then a pi will do you proud. I have several of my own and with clients. The pi is not without a few internet streaming service options either --
http://www.maketecheasier.com/xbmc-addons-to-destroy-cable-bill/
ODROID I have not really played with and it is quite nice hardware from people I have spoken to, however nobody has it, fewer people make cases for them, addons for them (some of which you can even buy in real life), use them as a test base for the software...
if you want a fire and forget media player for your parents and want a hope of being able to find a 5 minute copy and paste fix then go pi. If you need all the power you can get for the watts and your "well I could have purchased a game instead" money then maybe look around for a different dev board option.