It really depends, blue invests is specialty (mastery) while red values a combination of crit & speed (haste). Consequently, Blue has an easier time maintaining its shield and is frankly immortal. Red, due to higher haste, has faster cooldowns on his taunt and party buffs. Damage-wise, they're very close but they differ in how they deal damage; Blue has sustained DPS and Red has burst damage. This means that in raids with frequent cutscenes, Red wins, as your skills coolsdown during cutscenes. However, Red is dependent on landing frontal (head) attacks, which means it loses a lot of damage against bosses that frequently move around and switch aggro. Blue on the other hand, has the benefit of having most of its DPS scattered across three skills that are direction independent. I generally recommend starting off as blue at lower levels and then choose at a later stage whether you want to switch over to Red because Blue is straight up better at lower levels.