When comparing NetBSD vs illumos, the Slant community recommends illumos for most people. In the question“What are the best open-source Unix like operating systems?” illumos is ranked 4th while NetBSD is ranked 6th. The most important reason people chose illumos is:
Illumos is completely free and open source.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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 Open Source
Illumos is completely free and open source.
Pro ZFS file system
illumos uses ZFS as its file system. ZFS is also a logical volume manager besides being a combines file system.
The main features of ZFS include: protection against data corruption, data compression, checking continuous integrity, high storage capacities support etc...
Pro Zones
Zones provide an isolated environment to run applications in. Processes that run in zones are prohibited to interfere or monitor any other activity in the system.
Pro Performance analysis and troubleshooting
illumos uses DTrace for performance analysis and troubleshooting.
Cons
Con Lack of drivers
It lacks drivers for some new devices.