I have in these pages named too many favorite fruits -- satsumas, sour cherries, crunchy apples -- to expect you to believe another one, but watermelon is ALSO my favorite fruit.
The juice, freeze-concentrated once and then frozen in an ice cube tray, is great with rum, tequila, mezcal, or Cynar.
The rind, well, you know about pickled watermelon rind (which is easy: peel the skin off, simmer until it's not hard anymore, and then use whatever pickling recipe you like), which I make with the addition of cherry or tropical punch Kool Aid and extra sugar.
The seeds are edible, and a snack in parts of Asia, though I'm not particularly a fan.
And the flesh, well come on -- you know how to eat a watermelon. But you can do more than just the obvious. If you happen to have a vacuum sealer -- I don't :( -- vacuum-sealed watermelon takes on a texture like raw tuna, and is often served the same way. You can grill watermelon, which won't fall apart the way you might think. You can use it instead of tomatoes as the base for gazpacho, barbecue sauce, or ketchup. You can add a little salt, or a little salt and chile, or a little ground up worm powder, all of which enhance the basically bland flavor of the melon. You can dehydrate it, but the truth is I don't find dried watermelon all that interesting, and it takes a long time -- watermelon is about 90% water.
And me, I add tropical punch Kool Aid drink mix and sometimes a little sugar.
There's no seedless watermelon per se -- the watermelon sold as seedless, which up here has chased seeded watermelon out of the store, simply has immature seeds -- and seeded watermelon tends to be a richer red, and have a fuller flavor, or maybe it's just my imagination.
The easiest way to chop up a watermelon that I know of: if it is the size of a schoolroom globe or smaller, cut it in half; if it's long and oblong, you may want to cut a section out of the middle as well in order to make three or four pieces. Deal with each piece thusly: place it flesh-side down on the cutting board, and cut the rind off in pieces, from the pole to the cutting board. You can make both horizontal and vertical cuts to chop up the resulting block of flesh.
If you want to use the rind, it's easier to peel the watermelon before doing this, although I find that there is usually one section of the watermelon which for some reason is easier to peel than the others, and stick to that and let the rest of the rind go to waste.