For flowerbeds and shrub border I cover the ground with landscape fabric and cover that with a thin layer of wood chips. If I don't have any wood chips then I cover with fallen leaves. If I have the time I grind those leaves up with the lawn mower first to help them pack down better. The secret to using landscape fabric is to cover it with less than an inch of mulch - otherwise weed seeds just sprout in the mulch and you haven't solved your problem.

For the veggie garden I mulch with straw from bales. I prefer to let it rot somewhat because it is easier to break it off the bales into flakes that stay together while I fling them around the seedlings. I usually cover the veggie garden with black plastic that has holes cut in it every foot or so and cover the plastic with the rotting straw.

Most plastics degrade with sun exposure. Most irrigation plastic has been treated to withstand UV radiation from the sun but it still will last longer if covered under mulch. But the emitter holes or lines will clog if buried so you have to set things up carefully and then flush the system - it is hardly the "set it up and walk away" type of deal.

I wonder if the weeping form of hoses rather than the perforated type would be longer lasting and less likely to get clogged?

I use coarse hardwood mulch for my shrub and perennial beds and wheat straw for my veggies, in most cases. I get the hardwood mulch cheap at Charlotte's compost central...put down a 3-4" layer every two years and top it with a thin layer as needed in between. I've got soaker hoses under the mulch...works well unless I accidentally find one with a shovel, which has happened several times (maybe I should begin marking where they're located?!?!). I use clean wheat straw for my veggies...primarily 'maters, peppers, cukes and squash. I have 3 raised beds and containers so plant pretty closely, which eventually gives me dense shade under the plants, so the straw is really for moisture control rather than weeds (except the first few weeks when plants are small). In my beds I use soaker hoses under the straw...I have drip lines for the containers, with emitters under the straw. If you put your irrigation above the mulch, a LOT of it will just soak into the mulch rather than the soil.