When comparing Slackware vs Haiku, the Slant community recommends Haiku for most people. In the question“What is the best desktop OS?” Haiku is ranked 17th while Slackware is ranked 18th. The most important reason people chose Haiku is:
After about 6 years since the alpha version, beta has been released on Fri, 2018-09-28. Check [here](https://www.haiku-os.org/news/2018_09_28_haiku_r1_beta1/) for release notes.
Ranked in these QuestionsQuestion Ranking
Uses stable, plain-vanilla packages from upstream.
Pro Ideal to learn more of Linux
Pro Package management
Uses standard tar archives with shell scripting as packages.
Pro One more distro which is init based
Some users don't like to install systemd based distros because they increase booting and processing speed.
Pro No systemd
Pro Strong adherence to UNIX Principals
Con Not User Friendly
Con Large size live ISO
One need to vain 3GB+ data for downloading one slackware ISO.
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.