What would work the best to divert water from a down spout ?

Here is one site's suggestion. What works best is the individual solution for your specific situation and what you have available. I use flat rocks from elsewhere in my yard.

Another piece of downspout pipe or something like this:

It depends on the area. They make an expandable diverter that attaches to the downspout. You can make a small rock path for the water, or they sell plastic ones. If you have outside watering needs, you could always put in a rain barrel.

we solved this by digging a shallow trench. Filled it with rocks andlinedit with cinder blocks. You have to weed periodically and rake the leaves out if you have a lot of trees.One a year on the weeding and raking did the trick.It was inexpensive and not really to labor intensive. If you have a flower bed where the spout come down just make the trench a long as the bed is wide.Only downside for us was when we got a good old Texas gullywasher we had to retrieve some of the rocks and put them back.

4" PVC works or Corrugated flexible drain pipe it bends