I edit a lot of plain text in the course of my work: source code, HTML, etc. I also often use regular expressions to massage plain text and HTML into shape, search/replace, etc. Thus a good plain text editor is essential for what I do.
I use BBEdit daily for all those tasks. It is an indispensible tool for me and I highly recommend it.
Through Jan 14, BBEdit is discounted using code WINTERFEST2018 and costs only $39.99.