Once again, purchase order is Slot 1 --> Slot 6. Which slot you put them in is entirely up to you.
I usually start with [Guardian's Ward] and fill it with [1 Minor Strike] & [1 Lesser Health] [1 Lesser Health]. That'll help you get a leg up early game. I'll keep [Guardian's Ward] until I purchase my 5th card, [Amulet of the Veteran]. I'll sell the ward to finish the card almost immediately.
Normally I use another Tempered Plate in Slot 6, with [3 Beta Guard] & [2 Guard] [2 Guard] because your physical armor will go through the roof.
I rely only on physical armor to prevent melee fighters from destroying you in a gank. I don't worry about energy Casters at all. I do keep a [3 Thorned Greenweave] with [3 Beta Barrier] & [2 Strike] [2 Strike] as a back up though. Along with [3 Tuned Barrier] with [3 Beta Barrier] & [2 Barrier] [2 Health]. The energy armor cards are only there if their team is almost all made up of energy casters. Otherwise physical only to survive ganks.