I hope this doesn't start a war, lol:

Are there any differences between the two in terms of sound and/or quality? What are your opinions?

I'm afraid you hit the nail on the head about that war thing.
Oh Brother Randy, where art thou?

Difference in sound-usually
Quality-both good

Everything else is personal preference. If you're trying to decide between the 2, regardless of what anyone tells you, there's no substitute for you personally picking up and playing on a couple or more of each and deciding which sounds/feels best to you.

I agree with Bryan. It's more important to play the instrument you are thinking about buying. These are still hand crafted in many ways and although consistancy and high quality are in both, each instrument is unique.

Play them and then buy the one that "calls" to you.

I have a "cheap" guitar that I wouldn't trade for a $3000 Martin guitar because it plays and sounds the way I like.

Accordions are kind of the same way.

I also agree that it's a matter of preference. The only comment I have is that I have two Martins and two Acadians and I wouldn't say that the sound is better from either one but I do notice that the Martins are a little heavier and a little louder than the Acadians. I have not weighed them but I notice a difference. I would not give up either one but my next one will be one of Bryan's
Chuck from Kentucky

I have one of each and deciding between them is as impossible as deciding which family member you love more.

Like Chuck said, Martins tend to be heavier, and Junior tends to use tighter springs than other builders. Sometimes, I compare it to a Sherman tank. Tough and powerful.

My Acadian doesn't require as much muscle to play but is smooth and sleek. Instead of a tank, it's a Ferrari.

Do what you can to try out as many of each brand as you can.

Jude, you are right I forgot about the heavier springs on the base and chords especially. They are a bit harder to push. After playing the Acadian for awhile and then grabbing the Martin is when I really notice the difference.And when I come in playing the Martin my wife always says , why are you playing so loud...
Chuck from Kentucky

Keep in mind that heavy springs can be adjusted fairly easily.

Bryan, How difficult is it to adjust the bass springs?
I have never been inside of one.
Chuck from Kentucky

Wow Martin Ferrari Acadian Jalopy hope that answers the question. If you want to buy from a nice personable guy buy a Martin if you want the opposite buy Acadian.

I have a beautiful Acadian in C. Aged black gum

Its for sale!

What are you asking for the Acadian C ?

Well before you rule out all your options, there is a brand you might've forgot. Falcon made by Randy Falcon are some of the best I've ever played. I own 2 made by Randy and 2 made by Marc(Acadian) and I love my Falcons and would put it up against any great accordion. Hope this helps. -Cameron

I love all the accordions I own. I have a Heritage made by Rusty Sanner C# that is out of this world. My latest Acadian in Eb from 2010 is also a favorite (Marc has greatly improved his product, sound, volume and playabilty. No joke. Have a Martin in E that I love with all my heart as well.

I could go on, but I love all my accordions. Not all the same way, that's the thing. They're varying degrees of what I find awesome about each one.