As the campaign will start in the AEtonist West (a renaissance European area with religious and racial intolerance), the classes that make the most sense for starting characters are cleric, fighter, ranger, paladin, rogue, and bard. The world is tipped slightly in favor of fighters and rogues because they are the most "realistic" of the character classes.
In the West, Druids wouldn't necessarily be uncommon but will be difficult for novice players to play because he or she will be expected to come up with the religious belief system of the character. Druids in the World of Samoth are not the traditional D&D druids, but mainly fill the roll of spiritual advisor for uncivilized tribes that have not "converted to the faith". Most druid-like characters will be found among the countries of the eastern part of the West (Kovlich and Margova) and among the dwarves who have not adopted AEtonism.
Barbarians are very rare in the West, as most peoples have been "civilized" by the AEtonists. A barbarian walking around in furs and skins through one of the major metropolitan cities of the West is likely to draw many stares and will eventually be put to the sword as an uncoverted heathen. The easiest way to work a barbarian character into the game would be to create a background for your character involving him belonging to a tribe that was recently converted to the faith (AEtonism). Your character doesn't necessarily need to belong to the religion just because the tribal chief converted. However, all NPCs who encounter your character will assume that you are a member of the faith. If you go around announcing that you're not, you are going to get into trouble.
Wizards are very rare just because of the amount of money one needs for spells components, training, and research, not to mention the view of wizardry in the eyes of the common people and among the the AEtonist faith. Similarly, Sorcerers are universally feared by the common man. These characters are not barred from the game, but just beware that you're not going to take over the game and have an all-powerful wizard or sorcerer shooting fireballs in everyone's face all the time. I do allow specialists in all schools of magick, including necromancers and enchanters; however, there are some special rules for Diviners so please see me first if you want to create a Divination specialist. Note that, in Esoria, Wizards and Sorcerers are outlawed by the AEtonist faith and will be arrested on site and subsequently executed.
Monks are the most rare of characters in the West. The ancient martial arts techniques of the East were brought to the West during the Crusades a few centuries ago, and there are one or two schools in the West that have adapted these styles to the more crude Western style of fighting. Monks in Verundhi and in the Supreme Empire of the Golden Sun and Silver Moon are much more common. If you'd really like to play a monk, please contact me to discuss. Again, an Eastern-style monk will really stick out in the West.
