I bought a 3rd gen Apple TV, and I absolutely love it but...... Whenever I am at my Girlfriends house, her Roku just never stops blowing me away! Netflix, Crackel, Hulu Plus, Amazon on Demand, ect....! The content never ends. I'm thinking of selling my Apple TV to trade in for a Roku. I know Apple does not respond to these forums, but I hope they read them. PLEASE PLEASE PLEASE add more content.
I have both and have used both extensively. Roku is a far more reliable and diverse. Apple TV has a better Netflix UI and can handle higher quality video. Higher bit rate videos like those made from the apple TV handbrake atv3 setting push the roku too hard so in that case you get an unreliable experience, but that's not Roku's fault. Apple TV can be infuriating with iTunes sharing dropouts and occasional Netflix issues.
Some people claim their apple tv experience has been hassle free. I don't know if those people have cable or 100% rely on streaming like we do. For me owning both was the best decision. My recommendation is to buy a roku and keep your apple TV around for at least airplay. Besides who knows what future updates might hold for apple's black box