Figured I’d bump this older thread with some of my own observations. For my own general yard I use shredded redwood, gorilla-hair style stuff, but a bit more bark chips in it rather than just all finely shredded bark. It has a good balance of holding power on slopes but without turning into a singular mat. The latter can be a problem if you get a lot of rainfall because now you have a giant interwoven blanket of saturated mulch sitting on your hillside and it might be looking to make a move down it.
I used to use finely shredded cedar bark (very similar to redwood in composition) for all my plants in containers, raised beds, or planters but recently switched over to doug fir micro-bark (basically this stuff). I was finding that while the cedar definitely did its job for regulating moisture it was doing too good a job at it and after many cycles of watering would break down into a very tight mat that when bad enough you could water a container and water would just sit there for 20-30 seconds before finally being absorbed. Not even the usual hydrophobic stuff either, it had simply formed a tightly layered mat. There would even be times where I could water the entire surface of the mulch in a container, then break it up with my hands and there would be tons of dry mulch layers underneath the wet surface. The usual remedy to this is to simply break it up from time to time but it still kept a thin layer on the surface of the soil and I started to have concerns about both breathability and the evenness of watering so swapped it all out with micro bark nuggets which both breathe better and have better drainage.
I still use the shredded cedar within soil mixes as an organic amendment though.
Here’s an example of what I mean by the fine dust-like mat that has almost embedded itself with peat. This is after having removed all the mulch from the top layers:
And here’s a decent mulch study I read recently related to depth vs oxygen vs weed control and a few other variables:
mulch_225.full.pdf (646.7 KB)
There’s not a single plant I don’t mulch. The only time I remove it is if I have concerns about a plant having been over-watered or otherwise too moist and want to aid it drying out.