I like to stick with the class of character for my secondary skill set. Simply because when you switch classes you only get 20% of the skill. Which can be great at low levels, but as you build up. Those skill points need to be spent some place. As a Rogue I kind of depend on my skill sets being 100% or above. Just saying
The only exception that I can think of is the use of Spell Sword for the Warrior class. My question at this time would be, does the skill set build up your Spell Sword ability? If it does, cool. If it doesn’t the Warrior may want to change weapons. I don’t know, still playtesting it to find out.