I would go Ghoub to Kerry first of all then Cliff to Pastor as you need a DR incase you fail and then lastly Elviria to a Leader. Amber, Eyrik, Morphun, Eklore and Hugo work well it's up to preference.
Amber = Strong raw power but one bad move and your gone (I wouldn't use her past 6 survivor)
Eyrik = The most powerful Leader who can hold his own, he also makes the opponents pill and with 3 pills + he makes up for the attack you lose for not going mono
Hugo = Decent stats but 15 attack for the other 3 Rescue cards which can be great in later rounds forcing opponents to someitmes pill 3 just to get past bonus and power.
Morphun = Decent stats and works well in later rounds with Rescue because most cards need to pill to beat a Rescue and he gains well they spend pills.
Eklore = A great great under rated Leader. Think about it she is same as Morphun, cards have to use atleast one pill to get past Rescue and she takes atleast another one away so before you know it you will have same ammount of pills and you might even have more life.
It's up to you which Leader but definitly get one.
I would like to see players stick to the leaders they have been rewarded with.I believe this makes players stronger.I regret not experimenting more with the leaders I had at the time.I just kept on grinding until I had Ambre.like a lot of players I would imagine?