Oh, my answers:
We've had Netflix for years. It's cheap and the only downside is their catalog constantly changes, due to contract battles and what-not. We've played it through everything from an old Nintendo Wii, to now direct from the app in the "smart" TV, and also on iPads and devices when watching something solo. It works well and their algorithm for streaming what your net connection can handle (a big deal in the boonies on microwave ISP or on a phone or iPad on cellular) is top notch, probably as good as YouTube's similar variable bitrate stuff.
AppleTV. Used to love it for "real HD" quality stuff. No compression. Lately it sits mostly unused. Usually their prices are higher than pretty much anyone else. It keeps getting tons of updates lately for apps, but Cook isn't the content negotiator Jobs was.
Amazon Prime Video: Limited catalog but some excellent stuff scattered in it. And lots of regular popular stuff where first season is free and you pay for second season, or wait, and it becomes free and third season isn't.
DirecTV: I don't know what the word is for cable "un-cutters" but that's us. Our HD reception out here is "fringey" and while I have plenty of RF knowledge to fix it, my desire to repair all of the coax that ran everywhere that someone cut up years ago, was low. DirectTV installer got to do all of that "fun" work. Haha. Plus we hadn't built a media PC setup like XMBC and our schedules were leaning toward DVR style watching. So we splurged. By the way, their DVR thing with the mini remote boxes is incredible. Love that thing. Do the cabled remotes, not the wireless. The whole house thing "just works".
OTA HD: Works the best if you have good signal or are willing to work on it. True HD for local sports if they're on, etc.
Roku: Great option. We don't have one but family does, and it's a great all around box. Does all sorts of stuff. In our house, the Samsung Smart TV replaced most of what ANY box does, so these are slowly becoming unnecessary.
Samsung TV: Has all the big name apps except Apple. Of course. Even has some weird ability to remotely control Directv receivers from across the house if Ethernet is used and not wifi. Haven't messed with it, since it's sitting next to the Directv box. Probably makes a nice clean install if your wiring is in-wall.