At the moment it is Cresselia because right now its my strongest Pokemon. I am currently training Rotom, Palkia and Luxray at the moment and once they're at Level 100, Palkia will definitely be the leader.
When doing an urgent or incredibly challenging rescue, I use Palkia(max IQ of course). When doing a random rescue or mission, I go as myself(Cyndaquil), with my partner(Chikorita). And no, I am not evolving them.