When comparing NetBSD Default Light Desktop vs Haiku, the Slant community recommends Haiku for most people. In the question“What is the best operating system for a developer?” Haiku is ranked 5th while NetBSD Default Light Desktop is ranked 7th.
Ranked in these QuestionsQuestion Ranking
Pro Adhere to the standard
It adheres to traditional Unix and new defined standards.
Pro It's Open Source
It's open source with a BSD License, which is much more business friendly than GPL. It's the real ancestor of Mac, that is being used nowadays.
Pro It's real
Under NetBSD csh is csh not tcsh; also vi is real vi not elvis, nvi or vim. It's ideal for purists.
Pro Architecture portability
It's the most portable OS in the world when considering what architectures it can run on. It runs on very wide range of hardware, from toaster to satellites. This of course does not mean it supports drivers for many consumer facing products making it a difficult solution to just boot up and use when compared to other OSs.
Pro Clean source code
It prioritizes source code cleanliness over anything.
Pro Very Fast
Pro Beta has been released
After about 6 years since the alpha version, beta has been released on Fri, 2018-09-28. Check here for release notes.
Pro Only need 512mb ram
Pro Runs perfectly on old Hardware
Con Lack of drivers
It lacks drivers for some new devices.
Con No one uses it
It's a very niche OS that no one uses.
Con Small community
It is important when developing to be familiar with tools that other developers use. You can make any utility in any language you feel like, but if it's in an esoteric language that no one can read targeting a small platform that no one uses, then it was just something you did as a hobbyist, not as a developer.
This is not to say that Haiku isn't a great operating system to hack around on. Just don't delude yourself into thinking you're doing it to get familiar with tools that you need to know to be a better developer.
It's still in beta and quite unstable. Making it unsuitable for developing applications of any kind.