Are you starting in
Disneyland and then going to hop to DCA or will you be starting in DCA?
It really depends on what they offer food-wise. Some festivals have more popular (better) food than others. Locals tend to go on the last weekend to finish their Sip & Savor passes. The more popular the food, the more S&S they sell, and the more busy it will be on the last weekend.
Have you been to Disneyland for any of the festivals before? You can order and pay for all of your items, even if they are sold at different booths, at the same time. Your best bet is to go to the booth farthest from the entrance (usually near Golden Zephyr) and place your order there. The lines to pick up are usually shorter than the lines to purchase. Ordering early is always better. If you start in DCA, you can be in line to order right when they open and before the park hoppers arrive. That said, I wouldn't ruin the rest of my trip because I want to get in line for something from the food booths. Festival specials are often offered at restaurants throughout the park as well.
The image below is from the Lunar New Year map.
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