Since many rats care about the number of rats you have, cards like Pack Rat, Ogre Chitterlord and Vren, the Relentless are enablers and payoffs for the strategy, creating rats that grow in sequence with one another
Dex 38 Cards Most Expensive Mega Kangaskhan ex $60.53 M Kangaskhan EX $38.56 Kangaskhan $34.61 Distribution by Rarity
Cards that are too expensive (7 or above), too hard to cast, or just don't make an impact on the board will generally go in one pile per color
I'll run through the rest of the contenders here and talk about their pros and cons, but really it might all come down to the metagame you predict and the way you like to play the deck
A Digimon with 10% bond will transfer almost nothing during evolution, wasting all your stat-building efforts.Wrong Personality ChoicesUsing a Zealous personality (ATK/SPD focus) on a Digimon you want as a magical attacker severely limits their potential