Yeah, definitely not Saurus. Your two options basically are Kael or Tayrel. The traditional choice is to take your starter, so Kael, but since you got lucky and had Tayrel from a shard, you could also take him instead, as he's a better long term choice. And to be clear, after you take Tayrel/Kael to 5*, your next step is to take them to 6*, which will obviously take a lot more grinding still - but you could do the grinding at a higher stage then.
Based on your current roster, if you take Tayrel to 6* first, you'd probably still take Kael second, but perhaps by the time you get there, you will have enough better champions that you might just leave Kael at 5*, basically skipping the stage of the game where you use him everywhere. Perhaps also not. You really need a poisoner for the Clan Boss, so until you get one of the champions from the fairly short list of poisoning specialists, you'd still use Kael for that.