I’d go with an ergonomic one to avoid pain on the outside of the wrists.
I might be totally wrong, but I firmly believe these ergonomic risk factors are not the root cause of these health problems, and instead they are indirect factors that are correlated with fundamental problems affecting a person's activity.
For example, tennis elbow isn't caused by a particular model of a tennis racket, nor is jumper's knee caused by a shoe model. Interestingly, I stumbled upon a post somewhere in the past that pointed out that Emacs users had a higher incidence of repetitive strain injuries than vi users. One of the most basic treatments of RSI is a combination of working on the patient's overall posture and rest, regardless of keyboard format.
If you're experiencing wrist pain due to keyboard usage, the time you spend typing is a far more important factor than what keyboard model you're using.
Wouldn’t wrist position be considered part of your overall posture?
There are far more factors determining wrist position than the size of the keyboard, and only a very small fraction of all keyboard users end up developing any form of issue.
Moreover, I'd wager that the number of people enduring bad laptop keyboards greatly outnumber those developing any kind of RSI issue, let alone those who feel strongly enough to buy ergonomic keyboards.
It would be interesting to see how many ergonomic keyboards end up being snakeoil preying on people with more disposable money than good judgement.
There are far more factors determining wrist position than the size of the keyboard
Ergonomic keyboards are not a result of "the size of the keyboard", but the shape. The size could be identical, it is the shape that matters.
Without any real studies on it mentioned so far you're relying on gut feeling and logic here. Well, you mention sitting with proper posture actually helps, which is putting your body into proper alignment. That makes sense, if your neck is arched and your back is crunched all day it will eventually cause damage to your discs and cause nerve pain.
Why doesn't the same apply to your wrists? It seems logical that keeping your wrists cockeyed all day would put strain on them, and that keeping them in alignment would reduce strain.
At the very least it seems easy to see why some people would genuinely prefer keyboards like that just for comfort. I find it hard to label as "snake oil"
Ergonomic keyboards are not a result of “the size of the keyboard”, but the shape.
I apologize for the mistake. Even though I referred to size, what I had in mind was geometry/layout.
Without any real studies on it mentioned so far you’re relying on gut feeling and logic here.
Are there actually any studies suggesting that ergonomic keyboards prevent RSI? As far as I could gather, there's a correlation between higher RSI incidence and keyboard usage, but nothing suggests ergonomic keyboards lead to a lower incidence of RSI.