Which of these woods sounds best when played "unplugged"?

It's true.. if your bass sounds good unplugged, it can sound like a killer when plugged in.

But it's not just the wood ofcourse.. good wood + bad pickups = bad sound, period.

to get back to your question.. i think Alder is the prmier choice here.. Ash is more of a decorative-wood imho.

 

I have the exact opposite experience (opinion). To my ears, alder-bodied instruments don't really sing when played unplugged, but the wood really comes to life with a good pickup. Think classic Fenders. I would think it's the same way with poplar bodies (although the mile-thick lacquer on my MIM might have something to do with that choked acoustic tone... ).
My ash-bodied Yamaha has a very distinct unamplified tone, it really sings. In fact, I think it sounds more musical amp-less than amped.

Too little experience with other woods to make a statement on them.

 

Neither is better, just different. It's kinda like the rosewood vs. maple fretboard argument.

 

Maple sings the most to my ears, followed by northern ash, swamp ash, and then alder.

Swamp ash and alder are pretty similar in weight, although the weight can vary quite a bit from one piece of wood to the next. Northern ash is considerably heavier than alder.

 

Sounds better??

Then....what sounds good?? Or, what is "good sound"?

IMHO: get yourself an opinion of your own!

 

I own and have owned instruments made from ash alder bubinga mahogany poplar spruce walnut and plastic. I personally like the instruments I buy over the ones I didnt.

I look at an instrument holistically ie how does it sound when I play it through my amp?