short answer: LaTeX with Vim
Wordprocessors are easy to start with but highly ineffiecent.
Sadly Word became the widely used standard, so most are forced to use this $4!t or it's comparison of libreoffice.
With the effect that several hundreds of years of experience and science within typesetting - make the text best readable - are washed down the toilet within one decade for presumptive better looking but really worse readable text, because of typestting is done by people who even don't know, that something like this even exists, doing typesetting when they should write text....
(You may search for: "Wordprocessors: Stupid and Ineffiecent" for more and better details about this topic.)
Give Vim a closer look!
Long answer:
For someone really, really, seriously looking for an professional, powerful text editor there are only two choices really:
emacs or vi/Vim
I've worked with emacs many years. It's really productive,....but....
It not the question of "worse" or "better" (or even religious), it's the question "How are you structured? How do you think (top-down vs. bottom-up)?"
Most people avoid vi/Vim because without a couple of hours training you even can't do sh!t with it.
I think most ever rooted within a unix-like system knows the typical situations:
Your system does not fully come up for whatever reasons, all you need to do is to just add a single comment character before a line in a text file,
and all you got is this d@mnmotherdf0gging vi-crep!!1!!!1...'§"%$§=?§?$=!!!!!!!1111....
...looking for another - working - machine,
cursing,
looking for a vi-cheat-sheet,
swearing,
helplessly fiddling,
getting tourette-disorder
...it's known.
That's why most people don't give vi even a closer look.
And that's - maybe - the reason why the default editor on FreeBSD is not vi.
However:
With emacs I was not really completely satisfied. Personal taste.
It's not big, it's huge! Especially if you do the common emacs-noob's mistake and install directly ALL possible add-ons....("it's free..." - bad mistake, at least for a start with emacs! If you start with emacs, just stay at the basic-editor, which is very powerful for itself indeed, and only if you feel well versed in its using *ONLY* add, what you really need.
Otherwise you'll just drown in possibilties and non default-setting, wondering about which editor is the tutorial about
So I was looking for an alternative and again found many people praise vi/Vim.
After vanquishing my personal aversions against Vim I made the tutorial shipped with it.
It will take you at least 2 hours to even do the rudimentary basics badly, and it will cost you app. additional 20...30 hours to use ist nearly usable.
You have to force yourself to use it, otherwise you'll never learn it.
Yeah, it may be a little painful at the start.
But it's worth it!
And after 10..20 you've already managed the worst.
From then you start to master it.
After the first couple of hours you get a feeling, where the journey goes:
It's not that the editors a completely otherwise.
It's the fundamental principle how text is to be edited, that differs completely.
You better have to forget all what you've ever learned about texteditors ever, and completely start naive at absolute zero, trying to do as you never ever edited any textfile before.
To put it in a simplified picture:
emacs is like a big workshop with a vast range of tools.
For every editing task you have at least 3 tools (keyboard, GUI, scripting) plus additional tools for similar jobs.
So what your going to do is, look for and leran the suiting tools for you current editing task.
If you need/want another tool, you add more tools from a toolshop or mostly even a whole additional workshop.
You can use emacs directly from the start without knowing anything about it, because most editors are using the same concept:
editing and writing at the same time with a GUI.
But to be efficient - doing much editing work in lesser time - you'll have to learn the keyboard shortcut commands.
And you'll keep on learning for every new "tool" in your workshop.
vi/Vim is more like a small toolbox.
You cannot really do much with the tools alone.
And you have to learn them most of them first, before you can anything useful with it.
But you quickly can build with them any powertool or machine you need or want.
And there is no big effort in this.
Because you are sitting in front of an powerfull automation system.
Use it that way!
Another picture may would make it understand better:
Imagine you have never seen any written text nor even characters, and not the stupiest idea how to note you language.
If somebody shows you the alphabet, you'd say:
"That's a complete stupid load! First you have to learn all signs before one can do anything with it and second there are only 26 of them?! Are you completely mad?
Draw pictograms showing its meaning obviosly! You have to do no learning at all."
...and one day you figure out: Your drowning in thousands of signs, every single one either much work to paint or hard to recognize and distinguish.
And you receive additional problems like words cannot be painted, grammar etc....
The way looking easy for the start may not be the best chosen in the long term.
Understanding two things
1. The most efficient for editing lies in the power of the keayboard - whatever editor one uses.
2. Most of the time you are not writing - entering new text, but edit it.
That brings you to the idea of vi:
First editing is done - and only done - with the keyboard only.
(don't looking at GVim at this moment, because it's not a good idea to start with - you'll never grep the concept and Vim stays Ugh! for you.)
Second vi strictly distinguish between editing and writing.
And because editing is the most work you do, editing mode is the default mode that comes up at its start.
(The Esc-Key will be the most used key, because it brings you always back into mormal (editing) mode.)
The strict distinction between the two modes are very strange and Urrgh! because completely unfamilar for most users.
But is have a very great - not to be underestimated advantage:
Single keys are now editing commands.
So instead of cruising with your mouse around to menus or learning and pressing many more or less complex keycombinations, you simply have a dozen of very simple commands.
Those commands cannot do much for themselves alone, but you can combine them to quickly typed chains and so generate not only way more powerful commands but rather the exact edition command you need for this individual editing task at the very moment.
After I got the hang on Vim (yeah, it's not just coming to you - it's a hard way for a start, especially if you fall back trying to use your old editor habits)
I knew:
This is the editor I ever wanted.
It's small.
It's smart.
It's flexible.
It's tailorable.
It's customizable.
It's very logical.
It's intuitive.
It's powerful.
Very powerful!
And above all:
It's fast.
It's darned fast!
With no other editor you can become as nearly so fast as with vi/Vim.
Not a chance.
If you don't know Vim and convinced you are fast, try to get a chance to watch an experienced Vim-User at a couple of editing tasks.
You did not yet had even the slightest idea what fast really is!