
Blueluck |

There are good arguments to go with Bard, Druid, Oracle, Sorcerer, Witch, or Wizard.
What's most important to you, being accurate to the oldest "original" literature, being accurate to a particular vision of Merlin, or making a useful Pathfinder character who is Merlinesque?
I'd probably go with Druid for accuracy, since the oldest and most consistent power attributed to Merlin is the ability to change is shape. It also has the advantage of using wisdom (Merlin's primary attribute in the stories) and access to spells of healing & weather.

Carnox |

There are good arguments to go with Bard, Druid, Oracle, Sorcerer, Witch, or Wizard.
What's most important to you, being accurate to the oldest "original" literature, being accurate to a particular vision of Merlin, or making a useful Pathfinder character who is Merlinesque?
useful Melrinesque.
I'd probably go with Druid for accuracy, since the oldest and most consistent power attributed to Merlin is the ability to change is shape. It also has the advantage of using wisdom (Merlin's primary attribute in the stories) and access to spells of healing & weather.
PC is Paldin (Erastil, btw) so druid is out.

ZZTRaider |

Carnox, you may have missed it in the Leadership rules (there's a lot of information on that page), but it's perfectly acceptable to have a cohort with a different alignment than the PC as long as the cohort does not have an opposed alignment. In the case of your LG paladin, that means that the cohort can be LG, NG, LN, or TN without any issue. Otherwise, there is a -1 penalty to the character's leadership score, but that's it.

darkwarriorkarg |
Carnox, you may have missed it in the Leadership rules (there's a lot of information on that page), but it's perfectly acceptable to have a cohort with a different alignment than the PC as long as the cohort does not have an opposed alignment. In the case of your LG paladin, that means that the cohort can be LG, NG, LN, or TN without any issue. Otherwise, there is a -1 penalty to the character's leadership score, but that's it.
That's general. Specific Rule for the Paladin:
Associates: While she may adventure with good or neutral allies, a paladin avoids working with evil characters or with anyone who consistently offends her moral code. Under exceptional circumstances, a paladin can ally with evil associates, but only to defeat what she believes to be a greater evil. A paladin should seek an atonement spell periodically during such an unusual alliance, and should end the alliance immediately should she feel it is doing more harm than good. A paladin may accept only henchmen, followers, or cohorts who are lawful good.
I would go with a merlinesque LG witch or wizard and an Owl (Or improved) familiar. As a base, unless you need clerical backup.

Vod Canockers |

Doesn't matter what "Merlin" is, he will only speak in riddles, and show up when he wants and do nothing.
Go for Tim he's a better wizard.
It really does depend upon what you need him to be able to do, then find the class that best fits your needs. Short on skills/knowledge go with a Bard, need a good blaster wizard, etc.

Carnox |

This isn't necessarily a need based decision, but I'll give you some colour on the party makeup, etc. In any build he probably fills one of the kingdom slots better than an existing npc,
Baron is Paladin (Divine Hunter) 2/Bard (Arcivist) 3/Dragon Disciple 1 so far.
Rest of party:
Paladin (Sacred Light or something)
Sorc [creating a full cleric of Desna cohort]
2 x Rogue
Cleric (mostly)/Ranger (1 or 2 level dip)
A non-spontaneous Arcanist give us the most flexibility. "Merlin" will natural be off camera much of the time. He will probably "justify" a caster tower build from a story stand point.
And thanks darkwarriorkarg, you got to it before I did. I don't need my GM to waive the rule. Character has not walked the straight and narrow of a typical paladin so I'm happy to play up an LG cohort to help keep him grounded.