Trainee class, like the one in Fire Emblem or Ragnarok: A character starts with this job has sluggish base stats, but it has multiple class routes to take, and get a lot stat bonus to become a lot stronger with class changes. Trainee should be useful for people who want to experience freedom in choosing what to be in a more realistic scale. The class can also be useful to characterize a 'rookie' character. Other than that, I recommend the 'base 4' classes: Knight, Thief, Wizard, and Cleric. A knight has strong physical power and defense; a thief has speed and accuracy; a wizard can cast magic; a cleric can heal. They are all basic stuff which you can make them something of basic jobs. They are not as cool as other examples, but I don't think a free roaming RPG is complete without them.