The answer, of course, is it depends. The open D works very well for some tunes - it's often referred to as the "Reubens Train" tuning. I find the double D to be more versatile for playing with fiddlers, and it's a pain to re-tune in a jam, so I rarely use the open any more.

You can also tune the first string in double D up to F# to get another open D, which is fun for some things.

And there are probably several more alternatives!

Open D tuning is used in Bluegrass playing on some tunes, but I haven't heard an Old-Time banjo player use it. If you want to try tuning the banjo that way and experimenting, by all means, do it. I don't think you would want to replace Double D with open D. If you find you can play some tunes in open D, use it in addition to Double D. You can also drop the second string one note and play out of Drop D instead of Double D.

Use what works for you. I play mostly in standard C tuning. I use double-C and open D for certain tunes. You should be able to play comfortably in all 3. Your own musical taste and playing comfort should tell you which to choose.

I use double-D tuning (aDADE) for most fiddle tunes in D, but as others have noted, there are a number of tunings that work well for certain D tunes or songs. For instance, the open D tuning you mention has many variants, e. g., f#BEAD, which Tommy Jarrell used for Cumberland Gap. In this tuning, if you fret the 4th string, 3rd fret and the 3rd string, 2nd fret, you have the same D chord as the open strings in f#DF#AD, but now you can “walk up” to that low D.

Many other tuning variants like this are tailored mainly for just one or a few tunes, and are sometimes referred to by the name of one of those tunes (e. g., “Little Birdie tuning”, etc.). But only a few of those tunings tend to be useful as general tunings for D fiddle tunes, largely because of the typical melodic range of the tunes versus the range comfortably available in the tunings.

One advantage to DF#AD tuning is for singing. There are songs that never go below the they D note. If you don't have a mega-octave vocal range this tuning is useful. Try Wildwood Flower out of G tuning and then this one. In G tuning you go up the neck quite a ways, not so in D tuning. banjered

@swollenfingers

As a verifiable lazybones, I always choose easiest first. There is no right or wrong, and there are great options for each, so choose what you like. You can always change your mind, but start with easy.

There are several old-time clawhammer tunes that use f#DF#AD tuning (open D tuning), for example:

• Reuben: f#DF#AD has also been called Reuben Tuning, so it is the standard tuning for Reuben
• Peachbottom Creek (Wade Ward)
• Shortenin’ Bread (usually played in G tuning)
• Last Cold Whiskey (Ken Perlman)
• Little Satchel (Fred Cockerham) (but tuned up a whole tone to g#EG#BE on the recording)
• Frankie Baker (Fred Cockerham)
• Tennessee Line Hard Time , (Art Rosenbaum) tuned down to C: eCEGC

For clawhammer players the double D tuning seems to be the normal tuning to choose for D tunes, especially for fiddle tunes, but you may try open D. Sometimes it works, sometimes double D will be better.

To learn more about banjo tunings you may study this site: https://zeppmusic.com/banjo/aktuning.htm