I switched from Sickbeard to Sonarr last week and I'm extremely pleased I did. I had been finding Sickbeard missing or slow at picking up episodes, also clumsy for administration.
https://sonarr.tv/Sonarr is beautiful to use, closer to CouchPotato in its interface, its also done a great job of picking up episodes the momont they're released.
Also, check out this for an awesome feature, a realsed calendar of your shows, premieres, and if you've got them or not:
Fully recommended by me.