Mostly personal preference.
From a general point of view in elo;
Rescue is best as Mono.
You can never go wrong with a Mono Gheist deck.
Skeelz has really great abilities consisting of support, confidence and revenge. It's recommended to go mono skeelz.
Keep in mind to use cards with good abilities when making a half deck. Also when making half decks, use cards that aren't bonus dependant since a card might lose it's bonus half in the time in elo inside a half deck.