The answer is: the ones you actually eat. Small caveat, the ones you eat that don't require other parts that are detrimental to your health. If the only way you can eat veggies is some cut peppers on top of a pizza, or a tomato slice or some onions on a 1000 calorie hamburger, or a bunch of fried chicken and dressing on a salad, or a small amount of veggies/fruit with a lot of ice cream/sugar/etc in a smoothy, you'll defeat the point unless you also get drastic with cutting out other forms of calories/sugar. Oh, fried veggies (fried taters, onions, chips, etc) is another one, although the real problem there is how easy it is to overeat them.
Actually, I'd add a caveat and say start there, by adding veggies to food you like, and slowly work towards adding more (basically start shifting it so the veggies make up larger part of the meal). Or just start by eating raw the veggies you like and then slowly work to widen your palate by trying similar ones. Another trick is to combine them (pair veggies with sweet fruits, or other healthy things like nuts that will overpower the flavor of the veggies but aren't chock full of calories/sugar/sat fat). Smoothies aren't a bad way, just be sure not to go overboard adding sweetness/sugar (which is very easy).