I'm not sure if they're still affordable but I ended up getting both a morefine and a beelink, one with the n100 Intel CPU and the other with the n305. They handle everything I've thrown at them, and come with out of the box quicksync transcoding for Jellyfin/Plex. Handles 4K transcode like a champ.
Couple that with 2.5g Ethernet and they sip power.
Though they might have gone up in price since I bought mine.
Seconded ytdl-sub, especially if you want them to work flawlessly with Kodi/Plex/Jellyfin (integrated into the library etc)
Other than that, tubesync is nice and has a decent web ui too.
60% percent of the time, it works every time