Why not do a bit of both.
Memorise a structure. No not a "general" essay, just a structure.
See an essay is like a living creature, it needs a skeleton. (or an exo-skeleton, if you know what i mean heh..) Once this skeleton's in place it can be "accessorized" and "geared up" depending on the situation. For example all mammals are warm blooded this is a structure feature, but some have trunks.. this is an accessory; an adaption to the situation.
Therefore there are two "umbrella" components to an essay. The skeleton, and the accessories.
Memorize the skeleton for each "type" of essay you're going to write. (eg a hamlet essay, or a Belonging essay), also memorize the various "accessories", a bank of 20+ quotes per text, contextual information, main ideas of the unit etc.
DO NOT, memorize a fully accessoriesed essays! At most you're going to use... what? 12 quotes per text in an essay. This means that your "pool" of accessories to outfit your structure is vastly limited. It also means you've spent alot of your preparation time memorizing this limited pool. Going back to our the essay is a living creature metaphor, what your essentially doing when you memorize an essay is dropping an elephant into the ocean, hoping that somehow it'll learn to use its trunk to swim.
A better approach is to memorize the accessories separately.
Not only does this mean that you've got MORE options, because you now have a choice from bank of quotes from which elements can be specifically chosen and fitted onto your structure TAILORED SPECIFICALLY FOR the situation, but also itl'l be easier to remember, because instead of remembering one long STRING of words, you're remembering "chunks" of information.
(also after the essay's over youl'l have a pool of quotes from classical literature and contemporary film knowledge to make you sound smart, rather than an essay you're never going to write again).