I love all kinds of games and competitions.
Ignore the third game if you dig the art of the first two. MAJOR downgrade. They all have similar art, and Murdershroom Marsh has the best game mechanics. Is the art or the gameplay more important to you?
Skullzfire is easily the most expendable as it is the most basic of the three with no additional mechanics. I just use it as an introductory version of the game and then put it away.
Personally, I have built a deck that is 2/3 of Castle Tentakill and 2/3 of Murdershroom Marsh. I'm still fine tuning it, not that a game like this needs fine tuning, but I wanna maximize the interesting and more useful mechanics.