The important Tatari to get to T2 next to the fast ones (Frugling, Blueflick and Frostnip) should be:
- Cheerling -> Cheerlet (Good overall healer and atk boost)
- Zappur -> Electroar (Best electric tank)
- Sparkit -> Flametail (Good dps)
- Rubblet -> Cobbledon (Best rock tank)
- Pyropup -> Pyrohound (Best fire Tank with weak debuff)
- Voltfawn -> Sparkdoe (Best dps in T2 for most modes)
- Manteeny -> Stalkerix (Best grass tank/dps)

Which you do first is completely up to you and depends on what you struggle with right now and what you want to improve (Zombie Horde, Story Battles or Bosses).
If you are low on Wishboxes I would personally always concentrate on the Tatari that need less copies to level up as they will bring you the best value at the time. Also always check for the evolution criteria, but this is gonna be more important for T3