I've got a nice green piece of mountain ash, but have heard that carving ash is slow, tough on tools, generally not worth it. I wonder if it's still hard on the tools when green? I kind of doubt it but thought I'd throw this question out there. I like the dark heartwood.
I think it depends on what you are looking for. I think it carves nice.. I don't have as much experience with soft woods though. I carve a lot of ash and oak. I agree with the heartwood. It is very nice looking wood. If you want nice wood grain and are looking for sharp detail you will like it a lot. Just expect it to wear down the tools a lot quicker than you see with soft lumber.
Is there a difference? I know that due to the ash borer we have tons of it. It's known to fire wood guys as a tree you can cut it down, split it in the morning and burn it in the evening as it tends to be so dry. Your chain needs to be sharpened well and very evenly. Your soft woods you can get away with an uneven sharpening job, but in your hard woods it will beat the hell out of you if your rakers are too aggressive or uneven.