There is a huge variety of sets in The Elder Scrolls Online, with more being added every few months in each chapter and DLC. However, some of The Elder Scrolls Online's most popular suits are actually from the base game, such as Magicka and the Sorrow suit for the caster's mother.
The Mother's Sorrow set is the go-to choice for many builds, especially for wizards and other magic-based builds. While its two-piece bonuses are fairly mediocre, the power of this set comes from the three latter bonuses, each of which can greatly affect a player's damage output.
Equipping two pieces of Mother's Mourning suits, players can obtain ESO Gold, which is equivalent to three or four attribute points. However, with 3, 4, and 5 items equipped, the Mother's Sorrow set increases the critical strike chance by 657 per player, for a total of 1,962 critical strike chance. The full set bonus has no prerequisites, making the Mother's Grief suit one of the most versatile in the base game. While other sets may be more useful for certain builds, the Mother's Grief set is readily available and serves as a good entry point for further gear upgrades.
The Mother's Sorrow set only appears in the Overworld Deshaan, where the Fortress of Sorrow is the capital of the Ebonheart Pact. As such, fragments of the series can be found in many places throughout the region, including Delve/World/Public bosses, quests, and Dark Anchors throughout Deshaan. Fragments dropped into this set will increase to 160 with the player's level and championship points. Be sure to level up your character to this point to maximize your ESO Gold from this set, as the lower level versions just don't cut it in endgames. Similarly, players can also directly Buy ESO Gold on IGGM.