NC5 is horrible.
NC4 is way better.
Also Volkov (Not Volcov!) Commander is pretty cool - uses way less memory and it supports copying/moving of multiple highlighted directories which NC4 doesn't have.
I never liked DOS Navigator.
Back in the day I've been finding both - the transfer over serial connection and TERM90 very useful (first for copying lot of stuff from friend's computer to mine, second for BBSs 😀 )
Norton Utilities also has some very useful DOS tools.
I liked the FrameWork 3 /4 software suite (text editor, spreadsheet, database) I also liked MiniTAG text editor.
I used NeoPaint and NeoShow heavly. I also liked Envision Publisher for printing stuff as it offered near-inkjet quality on 9-dot matrix printer.
When it comes to diagnostic software CheckIt 3.0 is my favourite for legacy stuff and NSSI 0.6 for more recent stuff. But I like PC Doctor 1.5 as well.