I think most people would agree with me in saying that Sorcerer is definitely the more powerful of the two. Fireball deals a significant amount of damage and has a ridiculous range, and frostcall also shares those same points.
Cleric is pretty much entirely support, but it’s a lot harder to grind up. Your main damage abilities will still be your mage abilities (specifically Magic Bomb and Thundercall) and you’ll basically be relying on weapon perks and skill variants to get you through the first while. On the other hand, you also get the ability to heal and even revive others, which could be good if you enjoy playing a supporting role rather than a heavy damaging one.
Really, it’s up to you. If you prefer to deal a bunch of damage, go Sorcerer. If you prefer playing a support role and helping others, go Cleric.