This game is kind of unusual for it's leveling part(at least for me who play GC and GD). To get the best/highest stats card, you need to raise the cards to max level.
Here's the steps :
Get 2 identical cards in this case I'll use 2 Android. In order to get an adroid, you will need 2 Mechanics and 2 Enchanter cards. ALL MUST BE LVMAX 30.
Combine(Amalgamation) them and you will get 2 Android that are stronger that normal Android combined with LV1 cards. (Note that this process is 100% for now.)
Raise both Android to LVMAX 40.
Buy Arcana Succession from the shop. (Medals are received from Quests or selling Rare or higher cards)
Evolve the MAX Android with the other MAX Android, MUST USE Arcana Succession! This will add another 5% stats transfer.
Now level her up and TADA! You should get highest stats possible without burning lots of +atk/def arcana. As you can see from the pictures comparing the one evolved with LVMAX Adroid and the other with LV 1.
NOTE : Maxing Relationship doesn't give higher stats.
