witch has best app compability and most stable.
wfw 3.11 or NT 3.51
WfW 3.11 can run 99% of Win16 programs (the other 1% being Win16 apps made for windows 9x; yes they exist). However, it can't run anything Win32 unless you install win32s, then it has very limited Win32 support. If you have DOS applications, you can try to launch them from Windows, if it fails, you can always fall back on DOS and launch it from there.
Windows NT 3.51 had full Win32 support for its time
, which means Windows 95 added API functionality that Windows NT 3 doesn't support. Therefore is has some
Win32 support but is far from from being able to run everything. It can also run Win16 apps through an "emulator", and is probably able to run most Win16 apps, but not all. Since it's not based on DOS, you can't quit Windows and launch a DOS program from DOS, you'll have to rely on its "emulator" (NTVDM), which is virtually the same as Windows NT4/2000/XP/Vista's (and it's the same for Win16 apps as well).