It's your question, you have to answer it. My ears have lost some of the high end hearing, so a double melody string makes the melody clearer for me. After 40 years playing 12 string guitars, my fingers don't shy away from doubled strings. But you need to please your ears and hands. I added a fifth string to one dulcimer so I could double the middle string. I tune it to D Aa Dd, most of the time. I play the melody on the middle strings when I need a 155 tuning, and on the melody strings when I need a 158 tuning. But sometimes I use other tunings. My answer cannot possibly please everyone, but it pleases me. You need an answer that gives the dulcimer do what you need it to give you, not us.
I broke a string on my 4 string folkcraft dulcimer, so now i'm playing with 3. I like both ways, but it is easier to play it with the 3 strings based on the way I play. Once I get around to putting on my new strings I'll install the 4th (can't leave one lonely string in my package). 
I do three on all mine as well, as I end up using the melody string as drone as often as for melody. I've even gone so far as to remove the additional tuning machine on the dulcimers that are set up for four -- the hole makes a great place to tie in a strap for the instrument!
I did four strings for many years, and can see why someone would want to go that way too. As everyone is saying, it simply comes down to playing style and preference.
I only use 3 stringson most of my dulcimers,and if I therefore have an unused tuner,it makes a handy spot to attach my Snark!
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Jan Potts, Lexington, KY
Site Moderator
"Use what talents you possess; the woods would be very silent if no birds sang there except those that sang best." Henry Van Dyke
Depends on definition of 'better', '3 string' and '4 string'. Plus, what's 'better' for me probably won't be 'better' for someone else or a different situation.
I have both 3 string, single melody string and 4 equidistant for both strumming and fingerpicking. I have 0 of 7 set up with double melody strings. I doubt I'll ever have a 5-6 string MD as I don't really care for the sound of double strings.
This is a doozie Brian I play noter / drone style, but prefer a single melody string. 2 of my dulcimers are in fact 3 string. A recent acquisition is a 4 string, but equidistant with a single melody string. But that's just my own preference.
I'd go with 4 just because with multiple notches on the bridge and nut you can have paired melody strings, paired middle strings, 4 equidistant or leave off one and have 3 equidistant. That being said, I like 4 string equidistant probably because that's what my 1st one was (is; I still have it.) Yes, as many have said, it is a matter of taste and what you get used to in playing.
My preference is 3 strings. As others have indicated, though, it really is just a matter of personal taste for any number of reasons.
I'd say a 4 string dulcimer that has the option on the nut and bridge to be strung as a double melody string and two drones or to string as a 4 equidistant string set up.
Now having said that, I remove or drop one of the double melody strings and play only 1 melody string in my finger dancing style, or lift one melody string over and set up as a 4 equidistant configuration and still play one melody string/finger dancing.
But neither a 3 string or 4 string set up is better across the board, they are simply better options for different playing styles.
Currently I am using 3 string because it is easier to do hammer ons and pull offs with a single melody string. This is for chord/melody style playing. For my noter/drone playing I use 4 strings most of the time. So I can't choose A or B; I need to choose both A and B.
Ken
"The dulcimer sings a sweet song."
But to commit to an answer, right now 3 strings are right and the best for me on Treif, my four string Clemmer dulcimer.Smiles to you.
I think the answers above are all correct, Brian. You're asking a question about two different experiences. That is like asking if a car ride or motorcycle ride is better through the mountains. They are much different ways to enjoy the mountains. If I am taking your in-laws, then I take the car. But these days I'd rather just ride.
Big smiles to you.
The correct answer is: YES
Brian, it depends. I took off the extra melody string on my Cabin Creek because I was splitting the strings. It is easier to chord for me with just the three strings. My Prichard only has three strings. That's the way they made them way back when. With the piano strings Kevin put on it I do not lack volume at all. I just recently acquired a used McSpadden and have left the double melody strings on it. They are a bit closer together than the double melody strings on the Cabin Creek. I don't seem to have trouble splitting the strings on this. It's also has slots to do equi-distant but I'm not ready to venture into the dark side yet, LOL. I have taken a couple of beginner workshops and the instructor recommends taking off the extra melody string. Hey, try it both ways and see what suits you.
