Tower

The Tower is a Location unlocked after a players first Meditation. It features various upgrades that can be purchased with Arcane Essence.

Strategy
I feel very strongly that the best order to get these in is in the order of the list that follows. There are some other strategy decisions to make that could effect the order you take these in. For instance, with the Orb of Momentum turned on damage boosts are less critical. With the Orb turned on, perhaps speed would be more valuable.

Healing is more beneficial than Aegis, because it is more generically useful. Following that, if you have a chance to take Bravery or Alacrity, you should do so. Aegis is much better than Bulwark because it helps solve certain major problems with respect to specific enemies, and you can't get to the  other  damage buff without going through Alacrity first.

Therefore, especially for the first time through the game (before New Game+) and the second time through, the first four picks in this list should always be in this order.
 * 1) Tower Left: Healing
 * 2) Tower Left: Bravery
 * 3) Tower Right: Aegis
 * 4) Tower Right: Alacrity
 * 5) Tower Right: Retribution (this assumes you can get to the next one on the same run; if this is the last one you get during this game because your next mission is to kill the Doomstone, you could consider taking Tower Left: Bulwark instead)
 * 6) Tower Right: Precision
 * 7) Tower Left: Bulwark
 * 8) Tower Left: Haste