The sweet spot technically for me was probably later Solaris with things like zones and dtrace that nobody else had. The popularity of Solaris also made it much easier to find help from other people, Makefiles that just worked, SSL accelerator boards, etc. Ask anyone that worked with zones, for example, and we find all the buzz about docker and linux containers quite funny.
I probably hated AIX the most. It was tantalizingly close to other Unix implementations, but with enough differences that things would sort-of work, but not really. To be fair, there was a "right" way to do things that worked, but I was naturally trying to use knowledge I already had. It was also the platform most likely to bomb out when trying to compile open source software. Lots of tweaking makefiles, environment variables, compiler flags, etc, to get things to work. They had a sysadmin tool called "smitty" that I particularly hated.
I’m not really old enough to be an actual grey beard, but I got just enough hands-on experience with late-period Big Commercial Unix to feel like I at least swept floors and fetched coffee in the exclusive club. Cool, even if it was frustrating at times.
I guess that is the thing: we’ve settled into a monoculture that makes me deeply uncomfortable. NeXT won the desktop, but there’s only implementation. And Linux won the server. But in the meantime, I feel like only OpenBSD is credibly providing public infrastructure that everyone uses.
I kind of worry that we’re heading toward a world in which nobody really understands the guts of the systems that sit underneath modern cloud / containerized services. Furthermore, because that stuff isn’t as exciting as the Javascript framework de jure, the amount of innovation happening in the lower layers is nonexistent.
Edit: Well, also the security implications of the Linux/x86 monoculture.
Really? Mac OS has maybe 15% desktop market share.
In fact, I tend to develop on it since if it works on AIX it will be portable enough to work other places. That said, I like xlc performance but I despise its weird command line options. I mostly just use gcc on AIX also.
I do prefer smit to things like HP-UX sam, but I'm accustomed to IBM overengineering. ;)
One day I got an Itanium from Microsoft. It was fun to play with. Sadly I was forbidden from opening the server. It was so alpha that adjusting the clock would kill the server. It never went very far due to being so alpha.
Even though I haven't had to deal with Solaris in about a decade, and it being safe to do killall, it took me ages to break out of the habit of doing:
ps waxu | grep "[p]ython" | awk {'print $2'} | xargs killSo, intended for use by shutdown(1M) and nothing else. It's basically a completely different utility to the Linux one. They just happen to, unfortunately, share the same name.
AIX, if I remember right - it could have been HP/UX, seemed to be the one with the most broken out as extra cost options, like cc etc.
So Aix was the only UNIX where I was using import libraries and having to explicitly export which symbols should have been public.
The early 64-bit PC hardware was server grade, intended for NT and Linux. That set a standard, and then gradually people moved away from junk like Windows 98SE and Windows ME. Hardware bugs no longer had such an easy time hiding in a flood of software crashes.