In my opinion, it is hard to decide whether which of the two is more difficult to be put into an essay as both the quotations and illustrations can add value to it, if incorporated effectively but that is where most of the people fail.
People tend to use direct quotations when they think the idea cannot be expressed or communicated more appropriately. While some people just give a reference to it and paraphrase it in their own words, which sometimes loses its meaning or the level of effectiveness that original quotation had in it.
On the contrary, an illustration, I think, is more difficult to incorporate into an essay because it has to clearly express and bespeak in accordance to support the idea being discussed with the use of an evidence.
