So I heard NMM is the easiest way to install mods and make sure they work. However, I hear some say that NMM is really bad, and should be avoided.

Should I just start to use the Nexus Mod Manager to make things easier on myself, continue to install them manually or by the mods own .exe, or find another mod manager?

Not for Morrowind.
Install mods the old fashioned way, or with Wrye Mash Installers.

Thanks Pluto, that's what I needed to know.

Some info on http://wiki.theassimilationlab.com/mmw/Beginners_Guide#Using_a_Mod_Manager.

NMM can be used for Morrowind, the problem is that a good percentage were packaged with manual installation in mind. Meaning that many of the files are not organised in the correct format that a mod manager will recognize.