I would say any dressing you prefer. If you are looking to eat healthier, try some of the vinaigrettes. I enjoy the raspberry flavored, and I toss in some grilled chicken, nuts, and strawberries for more flavor.
Lots of different types of dressing pair great with this mix. My favorite is to mix a little bit of olive oil with red wine vinegar or balsamic vinegar. You save calories and fat by making your own. Sometimes I skip the oil and just use vinegar.
Whatever dressing you love. What my kids and I discovered is we drizzle it in olive oil and then use the Trader Joes Lemon Pepper grinder over it. We will even a lot of times do the olive oil and then just sprinkle it with salt....delicious! I never thought that would be enough flavor for a salad, but it is the perfect amount!