There are 8 different character classes in Durango: Wild Lands and each has their own specialities and each will give you a starting boost in a skill depending on their speciality. You do not have to invest the skill points you get on your characters speciality, you can for example pick a soldier and still level up the Weapon Crafting skill. The +20 boost is basically just a starting bonus. You can also unlearn 20 skill points per day and use them to level up another speciality.
There is no best character class, you can basically pick any character and use the skill points you get to mold it into anything you want. It is recommended that if you are new to the game to choose either the soldier class because of their fighting capabilities or the job seeker class because of their defensive skills which are particularly useful during dinosaur attacks.
Listed below in no particular order are the different character classes and their speciality.
Soldier
Starting Bonus: +20 Melee Skill Level
Soldiers specialise in melee combat and use their ability to master various weapon skills to hunt dinosaurs. Weapons that soldiers are particularly proficient at using are knives, axes, and spears.
Job Seeker
Starting Bonus: +20 Defense Skill Level
Job seekers recieve a big starting boost to defensive skills which is an important factor when leveling a character. Having high defensive skills are important to melee fighting as it enables you to last longer in battles.
Engineer
Starting Bonus: +20 Weapon Crafting Skill Level
Engineers are experts in crafting deadly weapons such as powerful bows and crossbows. This profession will also allow the engineer to make in-game coins by selling the weapons he makes.
Attendant
Starting Bonus: +20 Tailoring Skill Level
Attendants specialise in crafting different armours and equipment. Their tailoring skill gives them the ability to craft bags and pockets which enables them to gather things during their travels. Attendants can also make in-game coins by selling the clothing and armours they make at the island market.
Farmer
Starting Bonus: +20 Farming Skill Level
The farmer class have the ability to grow crops and they are able proficient at cooking different food recipes that give buffs that will increase the skill and strength of players.
Homemaker
Starting Bonus: +20 Cooking Skill Level
Homemakers have the ability to cook different types of food and drink recipes that give buffs that are especially useful before your party goes into battle. The farmer and homemaker class work particularly well when together.
Office Worker
Starting Bonus: +20 Building Skill Level
Office workers are experts at building things such as houses and fences. The higher the level of your office workers building skills the better the base they will be able to construct.
Student
Starting Bonus: +20 Gathering Skill Level
Students recieve a starting boost to their gathering level. Gathering is an important skill as you will need to gather plenty of things that are scattered around you as you level up.