All stats in The First Berserker: Khazan are useful but working on the best one can make your gameplay easier against harder enemies.

Vitality

• Increases Maximum Health
• Increases Damage of Attacks
• You can carry and use heavier weapons

Endurance

• Increases Maximum Health
• Increases Maximum Stamina
• Restore Stamina Faster

Stamina is the white bar and you need it for more attacks and blocks.

Strength

• Increases Maximum Health
• Increases Damage of Attacks
• Reduces The Damage You Take from Enemies
• You can Carry and Use Heavier Weapons

Willpower

• Increases Maximum Health
• Increases Damage of Attacks
• Restore Stamina Faster
• Reduces The Damage You Take from Enemies while Blocking their Attacks

Proficiency

• Increases Maximum Health
• Reduces Stamina Cost of Dodge

Best Stat

Strength is the best stat.

Because it increases your maximum health and attack damage. This means you have more health to lose and you won't die with one powerful shots, also you can kill enemies faster.