In my first run, Alakazam has had my back time and time again. Wonder guard is an amazing ability and has saved my ass many times. He also always manages to survive with just 1-3 HP, allowing me to go for the kill and winning many battles.
In my current run, I'll have to go with Cinccino. It still shines even in late game. High speed and attack IVs, the ability skill link and multi-hit moves (like tail slap, bullet seed and rock blast), making each of those base 125 damage attacks! It basically swept Charlotte once I got rid of her field.