Hey Matt,
I used the Princeton Review's Verbal Workout and Cracking the GMAT for AWA.
I did not practice writing essays for the AWA section. I just memorized a template for both essay types. When I took the real GMAT I wrote out my templates and filled in the blanks with supporting detail.
During the first essay my mind went blank and I barely wrote 4 paragraphs. I knew I probably received a 2.5-3.0 at the most for that essay. However for the argument essay, my brain was warmed up and I ended up writing 7 paragraphs. Per my official scores I received a 4.5 for the AWA.
So my advice to you:
1. Design and memorize the templates for both essays.
2. Practice writing essays using your templates under timed conditions.