I've been getting lots of iTunes gift cards, and I'm thinking about jumping into Apple TV. Since Apple is having their conference in June, I'm wondering maybe they'll announce a new Apple TV, and I should wait. I have a Roku, but obviously I can't watch iTunes movies there, well I think I can't anyway.
I believe the next Apple "keynote" is in June (June 10 according to Google). You may want to hold off till then just to see what they have planned where if nothing else if they announce the next generation of Apple TV you might get the current one for even cheaper.
Highly doubt a new one is on its way, or the difference will be negligible. The much rumored "AppleTV" that's literally a TV set, seems to have died off, or isn't coming anytime soon. The recent updates to AppleTV were 1080p and faster menus. Possible new features for this year might be dual-band wifi or 802.11ac, or more channels... But if you already have a 360/PS3 you'd have those networks anyway, and AppleTV already does HBO, Netflix, YouTube, Hulu, all the biggies. Roku this year added a better remote with private listening, on Apple though, your phone or iPod is the remote, and private listening could be done with AirPlay eventually. I think it's safe to get it now.