I'll echo a lot of what has been said on this thread but also add my two cents.
1. The lean/fat ratio does need to be about 80/20.
2. Ground Chuck is good, ribeye just has to be better, but it would be hard taking that cut of meat and grinding it for burgers (maybe not that hard). I probably would try it when Dom/Jewel sells the USDA Select Rib-Eye steaks or Rib Roast for super cheap.
3. I typically like a flatter burger and not when they plump up so much that they almost resemble meatballs. I form the patties flat and add the dimple (it prevents the burger from "shrinking up." I also am careful about not over-handling the burger and try to keep the mixture looser rather than compact. I minimize breakage on the grill by cooking the first side completely before flipping and never have a problem.
4. If I buy the meat pre-ground, I cook thoroughly (hence liking the flatter patties). If I grind it (using an old fashioned hand grinder), I can tolerate a medium burger.
5. Seasoning: I like salt/pepper and sometimes a little garlic powder and onion powder (wife's preferred seasoning).
If I'm really craving a burger, it'll be grass fed, 80/20 chuck or similar and self ground. I'll also sautee minced shallot in butter and mix into the burger patties with salt/pepper. Loosely form into a thin patty, with dimple. Grill on high, flipping once and add a nicely aged slice of cheddar. Add a nice smear of mayo on each side of the bun (as a fat barrier so the bun doesn't get soggy), and dress with mustard and pickle. A garden tomato would just be heaven but I'll have to wait. Ketchup is often too sweet but A1 isn't bad sometimes.
Good luck, let us know if your trials develop any interesting results.