Experts and BHG readers answer.
Thanks for writing. The best type of mulch really depends on yoru conditions and personal preferences. For example, in my garden, I use compost as a mulch; a 3-inch-deep layer of compost of the soil enriches the soil, smothers weeds, and its dark color really sets off my plants. (Plus it dries pretty quickly so I can walk in my garden without getting too muddy.)
If you have a slope, you'll probably want to avoid compost, though. The "pine bark nugget" type of mulch also doesn't tend to hold very well on a hill, but the shredded cypress or cedar mulch do tend to hold better.
If you want a naturalistic look, pine needles also make for a wonderful mulch. And contrary to popular belief, they won't make your soil too acidic for your plants unless you keep adding new pine needles to your garden every year for years and years.
---Justin, Senior Garden Editor, BHG.com