Titan Soul Stones can be easily obtained in a variety of ways.
Titan Artifact (Fragment) can also be obtained from Artifact Seal Chests and Elemental Tournament Shop.
Titan Artifact Seal are common to Fire, Water, and Earth titans, but different from Darkness and Light.
Totems can be leveled up with Guild War Trophies (or Emeralds).
Elemental Spirit Summoning Sphere can be used to obtain Totems.
Titan of Darkness and Light
Titan Soul Stone is a limited time event only (for the time being)
Titan Artifact (Fragment) are only available at Alter of the Elementa (for the time being)
Titan Artifact Seal are common to light and darkness titans, but different from fire, water, and earth.
Leveling up totems is done with CoW Trophies (or Emeralds).
Elemental Spirit Summoning Sphere cannot be used to obtain Totems.
No difference in upgrade
Titan Potion for all 5 Elements levels up
Titan Skin Stones (or emeralds) are used to level up Titan Skin for all 5 Elements.
Titan Artifacts level up with Essence of the Elements or Gold (or Emerald) for all 5 Elements.
Titan Artifact (Fragment) can be obtained at the Altar of the Elements.
Totems can be obtained at the Altar of the Elements, with the same emission rate and ceiling settings.
Hurdles for Darkness and Light Titan Upgrade
Titan Soul Stone is unknown next chance if you miss the limited time event.
Need to collect Titan Artifact (Fragment) only at the Altar of the Elements, and the expected value makes it more difficult to cunstantiate than Totems (although this should be resolved in the future with the shop unlocking)
No ability to reset the BLP with Elemental Spirit Summoning Sphere.