i'd go pc, i mean if you want any sort of multi-use without the thought of being tied down, then pc is the way to go, every other device limits you in such a way, it'll be fustrating. Sure sitting on a couch using a keyboard and mouse to navigate isn't as ideal as a remote, but if you were to go PS3, then you'd have to use a controller to navigate around and that's just silly, back and forward with the trigger buttons? not to mention tried watching netflix on a xbox? lol controllers were designed to fall off of coffee tables, try it, try to keep a controller on your coffee table in one spot for more than a minute.
Last time i checked boxee had a client for the pc, so that all your media movies and stuff could be controlled from the a boxee interface (much like the old xbox 1 dashboard) and there was a free boxee app so you could use a ios device or droid device to control it through wireless or bluetooth i think.
I use a htpc, i don't want to be limited by silly devices like an appletv, but it is not as user friendly as sitting back and using a remote.