I recommend reading the ESO DPS Tier List to understand what the strongest class in ESO is. This will give you a good understanding to pick your class, because depending on the situation the rankings can vary. There are plenty of activities in ESO and there is no class that does everything the best.
However, in general players like to pick a Magicka Nightblade, Magicka Sorcerer or Magicka Necromancer as the strongest class/ setup in ESO. I do recommend reading the explanation on the ESO DPS Tier List for further explanation.
