Your all-enclosing and probably not-helpful answer: it depends.
And do some research of your own. Like reading all those threads with hints at/for decks and possibilities. Heaven! You might even go look at the cards and construct your own deck... (Strategy now means letting other people make one a deck apparently. I feel the trend but do not really understand it.)
Morphun is good, because it helps maintain pill advantage, and in a 4 round fight, if you stick to 12 pillz, it gives you 3 extra for the KO bonus.
Bridget is good, because it helps you counteract some poison, and maintain minor life advantage... keeps you alive longer, and can decide a close match.
As for the deck, there are a lot of good choices for cards, I haven't made a Deck yet using the newer cards, as i haven't bought any in a few weeks, or maybe even a few months...
but, if you look into the power of each card, and their ability, you can usually put together a pretty good base deck.
if you construct a base deck, and present it on this forum, you'll find that people are much more likely to give you usable tips
Com on guys i needd more votes for the leaders and tell 1 k
and please make the deck