My advice on which character to select in a Single player game in terms of Difficulty, and Experience-

Predator Warrior: The most Balanced Character in the Game. Ultimately #1 Choice for Beginners.

Predator Hunter: Stronger than Predator Warrior, but recovery speed isn't perfect. My 2nd choice for more Intermediate players or if you are really getting bored with playing as Predator Warrior.

Lieutenant Linn Kurosawa: She must be the perfect choice for the more Advance players. She is skilled with great Martial Arts, nice moves to execute, not to mention devasting combos ! Rank as my 3rd Choice, do not underestimate this female Warrior !

Major Dutch Schaefer: Extremely strong but slow, I generally do not use him unless I have a Second or Third Player around.... Therefore only EXPERTS should really look forward to choose him in a Single player game.