Emacs. It takes a steep learning curve, but it’s been worth it.
A bit slow on the roemy side here, but I really like LyX. It’s not for everyone. Purists typically don’t like it, and that’s fair, bit it’s made life very easy for me, also in collaboration.
While I have Tex installed on my machine I always find myself going back to Overleaf. It’s full of useful templates and cloud storage really make a case for getting started fast.
I found TexStudio on the pop shop and I have been liking it. Before that I was just using vim with a few plugins.
A bit late to the party, but TeXstudio works well on a whole host of platforms, so it’s what I use most of the time. (Note: I also use Sublime Text for simple documents, but it’s not FOSS)
I’ve heard Emacs and Vim have a nice workflow for TeX as well, but I have yet to try either out.
For years I used TeXStudio. At the moment Kile is my favourite because it integrates so well into the KDE Plasma environment. Needed a bit of a setup to be useful for me, though.
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I prefer to use a general-purpose text editor rather than a LaTeX-specific tool.
Before it was sunset, I really liked Atom.io
Now I’m back to using the proprietary Sublime Text without much motivation to search for an alternative again.