It is somewhat understood that Evasion Skill > Evasion when you discuss which is better.
There is a reason for this.
The law of diminishing returns is applied by the game (it is believed) so that your +Evasion & -Evasion gear total is modified by your AGI and +AGI/-AGI gear and food.
So essentially, if you have +19 Evasion gear you may actually get +17 evasion or +22 evasion (ACTUAL) based upon your total agility. Evasion SKILL modifying equipment does not filter through this process, therefore you can wear Evasion SKILL equipment without having to also use slots for AGI bonus gear so as to not lose your bonus to evasion.
To put it simply: EVASION SKILL > EVASION
If anybody is interested in the formula, here it is:
(NATURAL AGILITY+AGILITY BONUS)*.05 = AGIMODIFIER
SQRT(EVASION BONUS) * AGIMODIFIER = TRUE EVA BONUS
NATURAL EVASION + TRUE EVA BONUS + EVASION SKILL BONUSES = ACTUAL EVASION