Well and SBD can carry one heavy bomb, up to 1,600 pound AP IIRC. and with a 1,000 pounder, can also carry two light[100 pounds or less] on the wing stations. Normally scouting mode was a 500 pound GP for whatever they could find to use it on.
The B-17 attacking an airfield canoe loaded to damage the runway and revetments or to destroy aircraft and surrounding AA guns. For runways, 1,000 pound GP with a slight delay is probable. For aircraft and guns, the 250 pound frag is preferable.
The B-17 was capable of carrying a much larger load in a short mission than for a long range mission Long range missions were normally limited to 4,000 pounds of bombs. Short range missions could carry up to 10,000 pounds or so. The other limitation was the bomb racks; a B-17G could hold at most: 2 2,000 pound bombs; 8 1,600 Lb AP; 6 1,000 Lb GP, 10 1,000 lb AP; 12 500 lb GP; 16 250 Lb GP or 24 100 Lb GP. This was limited by strength of the bomb mounts and the physical size of the bombs. The older versions were probably capable of similar weights.
Note that the 250 Lb bombs are "the most for the least" AND the 250 Lb GP was far and away the most used bomb weight because the explosive effect decreases about 8 times for a doubling of distance IIRC. I have the official documents buried somewhere. But having 4 250 Lb bombs drop in a Football field sized area was significantly more damaging {blast and fragments] than a single 1,000 pounder.