Any good organic mulch does the same three jobs: it holds moisture in the soil, keeps weeds from germinating, and protects roots from summer heat. The differences come down to looks, how long it lasts, and where it stays put.
Bark nuggets look clean and last a long time, but they can roll or wash away on slopes. Shredded bark knits together as it settles, which makes it the better choice on hillsides and in windy spots. Wood chips are economical and break down faster, feeding the soil as they go. Colored mulch is mostly about appearance, so it's best in beds where a uniform look matters.
Depth matters more than type. Two to three inches is enough to block weeds and hold moisture. Much deeper and water struggles to reach the soil; much thinner and weeds come right through.
Keep mulch pulled back a few inches from plant stems and tree trunks. Mulch piled against bark traps moisture and invites rot and pests. And if your home is near the hills in Los Gatos or Saratoga, fire-safety guidance recommends non-combustible cover like gravel in the area immediately around the house, with bark and mulch used farther out.
Most beds need a top-up once a year as mulch breaks down. Late spring, before the dry season, is a great time to do it, after the beds have been weeded and the edges cut clean.