I would only use Pine, not any other hardwood chips. Pine breaks down into the soil very nicely and does indeed help amend the soil. It is supposed to be good for both sandy and clay soil. After about a year, the pines break down into what looks like rich and fluffy soil. I love this stuff and so do the earthworms.
I always have a bag of Pine Fines and Fafard Pro Potting mix on hand. If I run out, I feel compelled to get more right away because I am always doing containers and amending garden areas. The pine fines are great in containers too, mixed in with potting mix. It has become so popular here at one of the small nurseries, that from time to time they are sold out and I have to wait until they get another shipment in. So when I run out, I make a quick phone call, and then head down to this nursery. Oddly enough, the big box stores and other small nurseries locally don't sell it. They are sure losing a lot of business by not carrying it at their stores.
