opinion: which is better.
In my own personal style of play, I prefer the paragon (pure) over the polymath(multi-class)
Since it varies by play style and every build is good for he or she who builds it, what style do you prefer.
All my toons are pure, but none, or at most one, are in a pre-built path.
I would rather focus on one role, customizing to my playing style, than either following a prebuilt character, or mixing and matching.