Yeah, can't pick just one. Like the fruit thread, often what I like most is what's currently in season since it tastes best at that time.
I'm growing some tomatoes and I can tell you nothing beats home-grown tomato flavor. Can't wait until it's harvest time for those (probably not for at least another month, month-and-a-half.)
I'm not going to split hairs on botanical technicalities, because with that argument, most things we consider "vegetables" are technically fruits.
Here's my list of loves in addition to the aforementioned tomatoes:
Eggplant (growing some of these, too!)
Butternut squash
Asparagus
Sweet potatoes
Arugula
Spinach
Kale
Carrots
Herbs (esp. cilantro, basil)
Sweet peppers
Avocado