ECO - I have enjoyed your comments here.
The Strain - I actually think it got better in season 2 and season 3 has been great. They started to tackle the mythology of the show in season 2 with the origin of The Master and have introduced new characters.
Z Nation - I may have stretched the better characters line a bit, but the top 3 characters from Z Nation could hang with the top 3 TWD characters. Z Nation has no Daryl-level character. Warren is a better leader than Rick. Z Nation doesn't do the Big Bads instead focuses on the mission - a cure for the zombie virus in the form of a zombie-human hybrid. It has probably 1/20 the budget of TWD. Look at it this way. Z Nation is to TWD as Vikings is to GoT.