There are many alternative keyboards to the standard US keyboard layout (called QWERTY).
Some examples include Dvorak, (and variants like Programmer Dvorak), Colemak, AZERTY, Workman layout, etc.
Do any of these confer a benefit to typing speed, accuracy or hand/wrist-health?
And, if so, which one of these should I choose as a touch typist if I am regularly programming?
Short answer:
If you are happy with your keyboard layout, stick with it.
Long answer:
I will try and aim to make this as definitive and explanatory an answer as possible. To understand a bit where I am coming from, allow me to express my own journey through this jungle:
I am a computer science student who started out with the German QWERTZ keyboard, typing at about 100 WPM (words per minute). When that turned out to be horrendous for programming, I moved to QWERTY. Then, I got taken in by the hype and turned to Colemak. After mastering it, I discovered there was a layout optimized for programming, and switched to Programmer Dvorak. Finally, still not happy, I tried to design my own keyboard layout semi-scientifically. And finally, now, I am typing these lines on QWERTY. (To save others the trouble and pain I went through).
Therefore, I will try to argue in my answer both from personal experience as well as from scientific published data.
The main arguments for all the alternative keyboard layout hype can be summarized to three major points:
Let's go through this one by one:
First, the argument that the QWERTY keyboard was designed to slow typists down is simply not true. It was nicely debunked in this question. The QWERTY keyboard was designed to stop the keys from a certain model of typewriter to stop jamming. Rest assured, we will discuss the "QWERTY is slow" myth in a minute.
Second, the ultimate argument that advocates of alternative keyboards love to use is that QWERTY causes Carpal Tunnel syndrome, because it strains the fingers. What's amazing here is that this is actually an Urban legend which has persisted despite it being discredited. See this question here. To quote from the answer by Graeme Perrow: "It seems that using computers in general does not cause carpal tunnel syndrome, regardless of the type of keyboard."
Finally: If QWERTY wasn't made to slow typists down and doesn't cause any illness, why use another keyboard? The answer usually offered is because other layouts are faster and have the keys aligned in a "smarter" way. We are told how much faster typists can be when they use Dvorak instead of QWERTY and how the home row of colemak offers great benefits to productivity and speed. We are treated to an avalanche of impressive-looking percentages, of how much faster and accurate you can be on an alternate keyboard, rather than a humble QWERTY.
However, if you look at hard, scientific evidence, you find... nothing worth writing home about. Indeed, there are two very interesting posts here and here: It turns out that the (very hard to objectively measure) speed gains are a measly 2% to 4%.
This mimics what I myself have experienced: If you are a trained typist, then switching doesn't give much of an improvement. After I had finally finished my switch to Dvorak, I was still typing at roughly 100WPM. If you want to go beyond that, you have to type a lot during your day.
I believe that the reason people observe a speed-boost when they switch is that they have to retrain their muscle memory from scratch. Which, if they do diligently, is rewarded with a faster typing speed. The irony is: I conjecture that if they had "retrained" QWERTY from scratch, they would have obtained the same speed increase.
Additionally, my own error rate didn't go down with Dvorak or Colemak. It stayed around the same level. Which, again, is not dictated by the layout but by the accuracy with which one has trained their muscle memory.
Lastly, on the note of programming: It is true that for programming languages, on QWERTY the keys used often, such as {}, [], ', =, +, -, _, etc., are all to be reached with the right pinky, which drags performance down. This still is not worth the switch to something like Programmer Dvorak, however, since, especially in programming, the limiting factor is rarely typing speed (once you get above 60WPM, that is).
So given all this, there are also a few downsides to switching that I wish to elaborate:
Dvorak suffers from the huge disadvantage that all computers use shortcuts (such as the famous CTRL+C and CTRL+V) which, on the Dvorak, are in different and hard-to-reach positions. Colemak doesn't suffer from this as much, since it kept the C, V and B key positions from QWERTY. However, even with Colemak, using programs which rely heavily on shortcut use (the most notorious of these being software like vim and emacs), has to be relearned from scratch.
Switching takes a very long time. Let nobody fool you. If you were typing at >80WPM, I can tell you from personal experience that it takes months to achieve this speed again. Even if you swap only a few keys (like Colemak), it is still a painful and long process.
When you successfully switch, you will be unable to type fast on regular QWERTY keyboards anymore (take my word for it). You will still be faster than someone who doesn't use touch typing, but if you ever have to type on a QWERTY computer as an alternative typist, you will be in for some embarrassment. This can get especially hairy if it is work related.
Many alternative layouts are not nearly as standardized as QWERTY. In other words: If you use an older machine, for instance, you may find your preferred layout not installed. This is a further hassle, because then you have to get around that problem by downloading and installing the layout you chose, meanwhile having to work in a layout you can no longer use.
Thus, in conclusion, my advice is: If you are happy with your current layout, keep it. The benefits of changing are much too small to consider. Especially if you are a QWERTY typist, I recommend staying with it. It will save you a lot of hassle and annoyances.