I've been on the fence with that for a long time. I only have cable for the internet, though I "think" I get some local channels with it. Doesn't matter, the resolution was so crappy, I use the $15 HDTV rabbit ears style antenna for local channels and it's fine.
For movies, I had Netflix that I would watch on the tv through a tether. Netflix started to irritate me (lost current episodes of AMC shows) so I dumped it.
We still have Amazon prime, but figured out they block streaming to a tethered ipad/iphone, which is shocking really. So...
A standard Apple TV will NOT stream Amazon prime. If you hack it, you can, but that's it. Research Apple TV 1 & 2, and you'll quickly find these older units sell for quite the premium because they can be hacked.
I really don't know much about Roku, but need to spend some time researching it before I throw down on an Apple TV2 that's only capable of 720P. I would suspect a hack for ATV 3 rev 1 is coming soon, but rev 2 was just released in March, and that sent all the hackers back to ground zero.
1978 13BT-40, 70 series mechanicals
1966 FJ45 lwb stock
2003 100 stock
1974V8J40, 1992FJ80, 1985FJ60, 1971FJ55, 1978FJ40, 1974FJ40, 1997 LX450 all long gone.