It's a great dedicated video/media player, but unless you're interested in PSN and PS3 games, a standalone player might be a better choice.
Then again, having a built in, user upgradable HDD, which can potentially be used for DVR functions in the future, as well as the ability to update firmwares via net connection...
I have over 200GB of video on mine; can't do that with a set top player.
But if you just want the cheapest player possible and only want to watch Blu-Ray movies, go with a set top box. If nothing else, it uses less power.