Through a long winded and boring series of events, I've got the Apple TV, Now TV, Google TV and a Sony smart Bluray.
The Apple TV doesn't do a lot without the iPad/iPhone, and I assume Macbook, but the airplay when used with those is excellent. It's great with Netflix and air video too, well worth it for that. We're looking at getting another. Shame about 4OD etc blocking airplay, it's all just a bit daft.
The Now TV is a bit of a lemon. It's very meh, seems to need unplugging and rebooting once or twice a day. I don't know if this is how it is with all Roku boxes but i'm not impressed, the Apple TV shows it right up. But it does get us Sky without having a Sky dish. It's on trial at the mo, i'm not sure if we'll keep it.
Google TV. We have the Sony £200rrp effort (included with a TV, I presume because nobody bought it). If that's as good as it gets it's a bloody disgrace. A complete waste of space and only used due to the remote being nice and the spare HDMI port. Junk.
Sony smart bluray. Does exactly what it's supposed to do, including playing everything i've thrown at it. It's going to stay.
Hope that helps... somehow.