IMO, each class (or type of class) should have one way to escape a grapple. Casters should be able to teleport away/entice the monster to let them go; rogue types should be able to wriggle free; fighter types should be able to break free.
Core 3.5 didn't provide enough options for this to work. Does Pathfinder?
Warrior types have the highest chance to escape grapples. They have the highest chance to break existing grapples, too. Offensive Combat Maneuver specialists (monsters with Improved Grab, for example or Warrior types with proper feats for improving grapple) may get better chance, while more defensive types just need to pack more Dexterity and deflection and dodge bonuses.
The easiest way to memorize formulas:
CMB = BAB + STR bonus + SIZE bonus
CMD = CMB + <stuff you improve your AC with> + 10
<stuff you improve your AC with>: anything you can add to AC excluding shield and armor bonuses
So, a naked 20th level Fighter with 20 Strength and 16 Dexterity who just took penis... sorry, could not resist... enlargement pill (to increase his size to Large) is going to have:
CMB = 20 + 5 + 1 = 26
CMD = CMB + 3 + 10 = 39
Were he to fight his identical evil twin (also size Large), he would need to roll 13 or more on d20 to Trip, Grapple, Disarm, etc, however his twin would find it pretty easy to break from grapple or use other maneuvers.
Obviously, size of your shoes, special feats and nice magic items could alter chances for both sides. You can also play dirty and use
Freedom of Movement (All combat maneuver checks made to grapple the target automatically fail. The subject automatically succeeds on any combat maneuver checks and Escape Artist checks made to escape a grapple or a pin).
The full definition from PRD:
CMB = Base attack bonus + Strength modifier + special size modifier
Creatures that are size Tiny or smaller use their Dexterity modifier in place of their Strength modifier to determine their CMB. The special size modifier for a creature's Combat Maneuver Bonus is as follows: Fine –8, Diminutive –4, Tiny –2, Small –1, Medium +0, Large +1, Huge +2, Gargantuan +4, Colossal +8. Some feats and abilities grant a bonus to your CMB when performing specific maneuvers.
CMD = 10 + Base attack bonus + Strength modifier + Dexterity modifier + special size modifier
A creature can also add any circumstance, deflection, dodge, insight, morale, profane, and sacred bonuses to AC to its CMD. Any penalties to a creature's AC also apply to its CMD. A flat-footed creature does not add its Dexterity bonus to its CMD.
Regards,
Ruemere