I'm taking a look at the cheapest three: Tablo, HDHomeRun, and AirTV, but you may want to spend a little more if you want a better DVR experience. Something like a TiVO OTA, or a Fire TV Recast, or the models listed above with a built-in hard drive, like the Tablo and HDHomeRun. The reason I recommend a model with a built-in hard drive is because there's little troubleshooting involved. They already have the DVR ready to go out-of-the-box. That's if you want DVR, or if you don't mind tinkering. The comparatively cheaper AirTV, HDHomeRun, and Tablo can have DVR, they just require an external hard drive, flash drive, or a more in-depth solution.
If you have a Sling subscription, you may be interested in the AirTV, as the box integrates the local channels with your cable lineup. However, reliability is a huge concern. The box was frustrating to use as I found it to be incredibly unreliable. One minute, a channel will come in just fine, but the next, it just can't stream the channel. It has nothing to do with the reception of the channel, the box just seemed to freeze up constantly. I found that when I switched to a different local channel, it would eventually come back, but not always. The audio and video quality of the AirTV is not fantastic. The audio is notably compressed, and the video isn't as sharp as it could be. And that's with the AirTV connected by Ethernet. When attempting to watch local channels on my Roku Ultra, it almost always resulted in the Roku requiring a restart, or at least Sling needing to be closed and reopened. the Fire TV worked much better, but it still wasn't reliable. The AirTV works with an external hard drive or USB flash drive plugged into it, but when trying to use it on the Fire TV, it would play the recording, but when I tried to fast forward, it would just go right back to the beginning. It's a shame this didn't work well because I would've loved integrating local channels in my Sling guide, but the reliability is just not there.
The HDHomeRun Connect Duo doesn't have WiFi or a USB port for an external hard drive. It must be wired to Ethernet and must interface with either a home server, NAS, or Nvidia Shield to get DVR capabilities. Keep that in mind when I tell you the HDHomeRun had the best ability to get local channels. The tuner is very sensitive, which is a good thing, because I was able to get a low-powered channel to come in very consistently, which I can't say for the other devices. That's a huge plus, as I'm only using rabbit ears for these models. The cons are going to be the HDHomeRun app, and how the app works. With use on my Fire TV, as I never used the beta for the Roku, the app initially worked fine on first few uses, but over time I found the app would lag with HD channels. The SD subchannels seemed to work fine, but on an HD channel, my Fire TV 4K Stick would stutter and delay the audio, something that wasn't because of reception. However, the HDHomeRun turns the channels into a very open streaming codec, so you don't need to use the HDHomeRun app. It can work with Plex if you already have a Plex server, and other media clients, so take a look into that. But keep in mind if you don't already have a home server, there's a lot more tinkering to be done to get the HDHomeRun DVR-ready. I'm not saying I can't recommend the HDHomeRun, but I can't recommend it to users who are uninterested in troubleshooting.
My initial complaints with the Tablo were its slow loading times to open the app on the lower-powered Fire Stick, but as far as I'm concerned, compared to the experiences from the other boxes, I'd just recommend you upgrade to a faster streaming device because the Tablo is my pick between the three. The Tablo gives you the option to compress the video to use less bandwidth on your network, through live TV, recording, and remote streaming away from home. I was under the impression that compressing the live TV would be a good thing to get rid of lag, but I found that only produced more lag. I'm not sure if the box has issues with compressing the video, but when I set the live TV to the highest quality, I found no lag occurred. I thought it was odd, but maybe it makes sense to someone else. Aside from a bland user interface, the Tablo was the least fussy smart box to set up. The best part is if you don't want to plug in an external hard drive, you can subscribe to cloud DVR service, making the Tablo an even better value. I just wish it worked a little faster on the network, and for the app to be a little more exciting to use, because then I'd 100% recommend the Tablo, over my 90% recommendation here.
In conclusion, of the three cheapest smart boxes, the Tablo was the best, but if you have the money, I'd still recommend you go for the TiVO OTA, or the Fire TV Recast, or one of the above with a built-in hard drive. The least tinkering and troubleshooting required, the happier you will be. Specifically the TiVo and Recast due to their impressive interface. Again, if you have the money, however, you may just want to stick with traditional cable where someone else has to set it up for you. Of the OTT cable services online, YouTube TV is the best because most of the local channels are included in the guide, but if you are like me and you like Sling's lineup more, consider the Tablo if you don't want to spend too much.