Homemade vinaigrettes are so easy that there is no reason to ever slather your greens in store bought dressings.
After I mix the ingredients together, I like to store mine in a small mason jar, so that I can shake it well before using (in case the oil and vinegar have separated).
The addition of a small amount of mayonnaise helps keep the dressing stabilized. I usually use Champagne vinegar, but a good red wine vinegar or fresh squeezed lemon juice will work as well.