Often, I'm asked about my favorite foods. And though I don't like "favorites" questions (I don't really have to choose, do I?), when pressed I always mention eggplant. This is ironic, in a way, because I didn't grow up eating eggplant, it's not widely considered a comfort food, it's not as easy to cook as most other vegetables, and many people don't like it at all. Furthermore, it's difficult to generalize about eggplant. They vary wildly in size (some are small as golf balls, some nearly as big as footballs), texture, flavor, seediness, and required cooking time.
Having said all of that, this is the time of year you're most likely to find good ones -- and even if you misjudge, there are a few steps you can take to make them taste good anyway.
With eggplant, smaller is almost always better; the best ones don't necessarily have to fit in the palm of your hand, but you're much better off with four quarter-pound eggplants (or even two half-pound eggplants) than a single behemoth weighing a pound or more. They should be unblemished and firm -- as with most vegetables, squishiness does not bode well. And you shouldn't buy them too far in advance of cooking them -- they might look indestructible, but they can turn lamentably soft after just a couple of days lingering in the fridge.
All of this should provide you with eggplants that are firm and relatively seed-free (the seeds are usually bitter). But if you find a number of seeds, or you just want the least bitter eggplant possible, you can reduce acridity (and wateriness, and therefore cooking time) by salting eggplant slices or chunks before cooking them: Put them in a colander in the sink, toss them with a tablespoon (or more) of salt, let them sit for an hour, rinse, and dry with paper towels.
There's another step that makes for tender and flavorful eggplant: Don't skimp on fat when you're cooking it. Sliced or cubed eggplant famously absorbs oil like a sponge, and you'll need lots to keep it from sticking to a skillet, baking sheet, or grill. But even with non-stick cookware, fat (olive oil in particular) is a fabulous flavor enhancer for a vegetable that doesn't have a particularly strong flavor .Olive oil also makes sautéed eggplant surprisingly creamy, as long as you cook it long enough so that it becomes meltingly soft and tender. I like to flavor sautéed eggplant with classic Italian ingredients -- garlic and basil -- but other herbs and aromatics are good, too, as are chiles (added to the oil at the beginning) or toasted nuts or breadcrumbs stirred in right before serving.
If you have neither the time to salt eggplant nor the inclination to add lots of oil, your best bet is to cook it whole, without oil, over fairly high heat, until the skin blackens and the eggplant collapses (a satisfying sight). You can do this in a dry cast-iron pan on a stove, in a hot oven, or (for a wonderful hit of smokiness) on a grill. After it cools enough that you can handle it without scarring your hands, scoop the flesh out of the blistered skin, chop it, and serve it as you like -- it's particularly good in salads and dips. You'll still want to add some fat for flavor, but don't feel tethered to olive oil. You can take eggplant dip in a Southeast Asian direction by adding peanuts, coconut milk, lime, and ginger. The results are creamy, nutty, and fragrant -- even when made with less-than-perfect eggplant.