I'm going to run with the crowd..number 3 for me.

I like number 4, but as has been said, I find the bokeh distracting.

Welsh Mountain Zoo!! Haven't been there since I was a kid!

Love number 2 and that water fall!!, I think you have it just right. Not a strip of "cotton wool", but still gives the feeling of fast flowing water.

We'd get away with 4

Ah...so that's why I'm still poor. I keep putting my money on the donkeys instead of the horses

Whoa!! Your timing has to be inch perfect for that. I think you are asking too much from this kit.

You are talking accuracy to within a hundredth of a second ( I'd have thought ). Difference in the speed of the horses could explain that. What sort of speed does a horse run at? How much distance can it cover in a milli-second? Where would that put the horse after triggering the LASER? What if it were a slightly faster or slower horse, where would that now place the horse?

All of these will have a bearing.

Here's a thought...
Are you always getting an image of a horse, but sometimes just the rear, sometimes the front?

If so, is the image crisp?

If so, what lens are you using? Is it the kit lens?

Would you be better with a wide angle prime, so the horse would remain in the (now larger) frame?

I don't know if this would be better, just my thoughts.

You beat me to it...I was just about to add the same link

Do you have auto focus turned on?
Just a thought, but is the camera trying to focus again, then take the shot?

Wasn't there a guy in the late 19th century who first recorded how horses ran? I believe he had a string of cameras, triggered by the horse breaking a cotton line. But, he had it set up so that the cotton didn't trigger the camera on the same post it was tied to, but on the next post. I can't remember how much room he left between the fence posts, but that might give an idea of how far back you need your trigger.

Remind me never come work for you

I'm with Malo and Hyram on that, I had yours down as the winner. Great pic