I would agree that of the 4 species being discussed, a children's python is most likely to be not-so-docile- and especially for a first snake, corn & rat snakes are better choices for ease of care too. That's very good advice, about starting off with a healthy yearling, if one can be obtained.
I looked at that link, & they list good choices for diurnal snakes- including gopher & "rat snakes" (in general- they didn't get specific). The thing to remember is that every species has pros & cons- and sometimes the best care & best results are achieved when a person picks what most appeals to them. (Gopher & bull snakes need large cages & are very active- some can be feisty too, or at least the ones I've known were expert at bluffing. My bull snake hatchlings were not, however, "bluffing"- They were quite sassy!)
As far as snake activity, the most active diurnal snake I can think of is a racer, such as a coachwhip- but for most people, they make terrible pets, lol. Very active & hard to handle without bites. Garter snakes are entertaining too, but not so much fun to "handle".
Remember too that most snakes are not "out in the open" all that much except when they're hungry, no matter what their "normal hours of operation" happen to be. Snakes are pets whose privacy needs should be expected AND respected- they'll never be a "constant companion" like dogs & cats, but they're still rewarding in their own way. They provide a window into nature.