I'd like to have everything in one place, accessible offline for reading and searching, preferably with markdown support.
Do you spend a lot of time in a specific editor?
If so, consolidate those text files into one folder, and use your editor. The only issue will then be editing them from your phone - I don't, I just send myself emails, and add those notes to my files once on a computer.
I might revisit wikis, specifically for notes I need to share with others, but even then, it will be one that supports a simple format like asciidoc ro markdown, so I can keep using an editor. I have tried several systems, and none beats the convenience of the editor you're familiar with.