What are the most important aspects to look at in a Morty?

Later on as the game progresses I will collect everything but right now I am trying to put together a really good team to level up.

What are the most important aspects to look at in a morty? I was thinking Stats Total? Rarity, Base XP, Base HP, Base ATK, Base DEF, Base SPD?

Basically another way to ask this question is, other than Cronenberg and The One True, what are the best 5 Mortys to put together in a party?

Base ATK and Base DEF