Oh, Boy! Fun subject!
I'm not sure what connotations the word creationism carries, so I'll steer clear of it for the moment.
I have concluded the universe was created.
As to proof, one must either be a witness to that creation possessed of both immortality and have excellent ability to recall something he witnessed a long time ago, or one must be able to experience communication with the creator(s) in order to receive testimony about the creation. So, proof sounds like a pretty tall order to me. Leaving not much else but conclusions.
I base my conclusions on just a few points.
Living things are the only things ever observed to act independently aka with self-determinism. That is to say, the physical universe (matter, energy, space) has to date always behaved predictably after man understood the factors involved. No cue ball ever changed direction mid-course unless acted upon by something else. The physical universe lacks self-determinism, it lacks creative ability. This alone is not conclusive, because it could have just 'happened'. Read on for the rest.
Living things however are repeated demonstrated to possess self-determinism and creative ability. For the longest time it seemed only Man possessed this ability. Recent experiments have shown a crow creating a solution to getting food out of a closed container. To check the theory, the investigator set up a mutli-step problem whereby the crow would have to recognize the initial problem, figure out a solution, then solve another problem in order to implement the first solution. Get it? Two problems to get the food. AND! The bird had to remember the sequence of problem, solution, problem, solution, food. The bird needed a stick to get food out of the container. But, the stick was behind slats and he couldn't reach it. So, he had to untie a hooked piece of wire, in order to get the stick to use the stick to get the food. And, that's what the bird did. And, there were no false steps, meaning he didn't get the hooked wire and go straight to the food by forgetting the stick. He took the hooked wire straight to the stick behind the slats, got the stick, and then used the stick to get the food. In other words, crows possess the ability to recognize problems and create solutions.
Chimps are already understood to do this sort of thing. Dolphins and other marine mammals talk to one another.
I have personally witnessed a gray squirrel playing alone with a stick--that is to say the animal was imagining (creating) combat with a stick. I've seen cats do it with rugs.
Only living things possess self-determinism/creative ability.
There is quite a bit of evidence that tends to support that Man is a spirit/soul inhabiting a body. All major religions share this in common--regardless of any other doctrinal differences. From a dispassionate viewpoint, whether souls exist is independent of religion. Just the same as religion has no bearing on whether water freezes when the temperature drops below a certain point.
There is a difference between the creative ability of a crow and a man. A matter of degree or quantity. A crow can create a little bit to get a snack. Some men create on a grand scale--buildings, canals, super-tankers, countries, navies, entire economic systems. Same thing--creativity. Its just a matter of scale between a crow's creative ability and a man's.
So, here we have a physical universe which cannot create, in close proximity to life which does create. I conclude that something living created the universe. Something capable of vast scale. Was it a single God? A super-soul? I don't know. But, I know there are an awful lot of souls right here on earth, a single planet in an observably huge universe.
A couple men can create an air-plane. Put a few thousand men together and they create a rocket that flies to the moon. See how the scale changes when the creativity gets combined?
I can't but wonder if it wasn't the combined creativity of a vast multitude of souls who created the universe. Maybe just to have a place to play, no?