Most of the time when I do a comparison like this I'll do it on a flat horizontal panel. Horizontal panels are the easiest to work with and take advantage of the sun's light giving us the best possible viewing.
Whether comparing waxes, sealants, or a wax and a sealant be sure to start the test evenly. What I mean by that is to wash, clay, and clean the paint to ensure you're giving the product the best possible condition to perform.
While you can use the entire hood for the test, you can also split the hoods surface into quarters or 4 smaller sections. Place a piece of 1/2" tape on one section splitting that section equally into two sections. Apply the products you've chosen to compare according to directions, buff, then remove the tape and compare the differences.