Whenever two of the same deck types (aggro, tempo, control) play each other, the strategy generally revolves around outdoing the other.
If you manage to gain the aggressive upper hand as an aggro deck, you're forcing your opponent to either out-aggro you, or force them to play more defensively (which their deck is not optimized for).
- Aggro vs aggro generally becomes a race. Burst power in the first few turns is key here. A player who notices that they are losing the burst race can feasibly try to switch to the first tempo strategy listed below, given an advantageous board to do so.
- Control vs control generally becomes a matter of who can flip the board on whom the most. Card efficiency is key here. If you can wipe a board that took 4 cards to build with a 2 card combo, you're ensuring having the upper hand in the late(r) game.
- Tempo generally becomes a game of attrition. Playing minions that are marginally better than the opponent's (but saving the better ones for later) is key to success. Each player can choose to approach in two ways:
- Minions keep killing each other and the enemy hero only takes damage after the board has been controlled.
- Players somewhat ignore each other's minions in favor of rushing the hero down (turning it into a variation of the aggro race).
As both are aggro decks, players are incentivized to try and rush each other down.
However, due to the nature of secrets (triggering only on an enemy's action), the mage will be more able to take a control-like approach to the game (faking secrets, subtly controlling the opponent's board).
The hunter, on the other hand, is likely going to be better off rushing as fast as they can. Their aggro setup is usually a bit more one-sided and cannot reliably be used for a tempo/control approach (when compared to the mage deck)
But both decks are still heavily subjected to draw. Given a bad draw (situationally useless secrets), a mage might end up unable to exert any control. Given a good draw, a Hunter might end up able to play a reasonable tempo game.