There are so many ways to mulch, and so many different materials to use. What's most important? Cost? Availability? Ease of use?
Your first consideration is to ask, what is this mulch for? If it's to hold moisture in the soil to conserve water, there are a few mulches that excel at this.
Sometimes, for pathways for instance, other
materials will work better, providing drainage, preventing slips and
falls, and giving a permanent walkway for wheelbarrows.
Some crops need temporary mulching, such as tomatoes, and once the season is done, this mulch needs to be biodegradable, saving you time and effort in the fall.
Tomatoes benefit from red mulch, which
reflects on the fruit, helping it to ripen quicker. As you might
expect, this would not be an organic mulch, but plastic. Dispose of it
responsibly, or get the kind that you can use for years without
This chart will help you hone in on the best mulch for your needs; compare the columns.
* It has recently come to my attention that hay and straw quite often has a chemical herbicide in it (aminopyralid herbicide, also known as Grazon), which is persistent even after feeding to cows and horses and other animals. There doesn't seem to be much evidence that using it prior to animals eating it has the same effect, but for now, I'm shying away from its use in my garden.