TheSorcereris our choice for the next best pick.
Each of Oblivion’s 21 prebuilt classes specializes in either combat, magic, or stealth.
Each class is outlined in detail and ranked further below.

Healer
Healers heal - and not much else.
They don’t start with any way to reliably deal damage, unless you go all-out with Destruction.
They have absolutely no proficiency with Blunt or Blade, meaning they’re squishy as heck.

Acrobat
Acrobats are agile combatants who specialise in using Agility and Endurance to outlast a foe on the battlefield.
Rogue
Rogues stab stuff and get by with the force of their personality.
The inclusion of the Rogue, alas, is rather redundant.

Monk
I like playing as Monks in other games, but the ready-made version in Oblivion isn’t great.
Hand-to-Hand just isn’t a great skill in Oblivion, alas.
They’re middle-of-the-road, but not terrible.
Archer
The Archer hits things from afar with their bow and is a straightforward, reliable class.
Warrior
Warriors are no-nonsense fighters who excel with all martial weapons.
I like them more than Warriors, but prefer Crusaders and Bards.
This is similar to the Assassin build in some ways, minus the Marksmanship.
Witchhunter
The Witchhunter’s like the Spellsword, but with a focus on archery instead of melee.
This would be a better class if it had some skill to bump up Endurance.
This is Oblivion’s take on a cleric or paladin, and it’s a good choice of class.
So, more of a swashbuckler than a bard in some ways.
Assassin
The Assassin kills stealthily without leaving any trace behind.
For stealth-based characters, this is the best ready-made class that you might choose.
A great class all-around.
For more on customising your avatar, check out our guides on thebest birthsignand thebest race.