Solaris 2.5 was a very solid OS and better than NT 3.5 in most respects unless a defining criteria for "better" is "runs well on PCs", which it didn't.
OS/2 was also a good OS for x86 PCs. At least as good as NT, unless, again, you want it to run software designed for Windows.
I wasn't really into OS/2 but I concede that it was probably about as good as NT at the time.
I would, however, much rather use NT 3.51 as a desktop OS than Solaris 2.5 with CDE and its 80s-style command line utilities (luckily it seems they are using GNU stuff nowadays?).
OS/2 was also a good OS for x86 PCs. At least as good as NT, unless, again, you want it to run software designed for Windows.