I've tried several different, SimpleNote, KeepNote, EverNote... and so on. I have come to a conclusion, that using the default iOS note app is enough for me. Using paper notes while @lectures and rewriting them sometimes to Notes.

I'm also using another method of note taking, which I prefer more, but which is not always accessible on the go. I stumbled upon a script here and modified it a little. (changed vim to nano and added some other):

    #! /bin/bash
    fpath=$HOME/notes.md

    if [ "$1" == "cat" ]; then
        cat "$fpath"
        exit 0
    elif [ "$1" == "rg" ]; then
        rg "$2" "$fpath"
    elif [ "$1" == "nano" ]; then
        nano "$fpath"
    elif [ "$1" == "--help" ]; then
        printf 'Commands: \n-----------------------------------------------\n
        $ notes \n
        $ notes --help\t\t--\tdisplay this help\n
        $ notes date\t\t--\tadd date row to notes\n
        $ notes <text>\t\t--\tadd new entry \n
        $ notes cat\t\t--\tprint notes using cat\n
        $ notes rg <pattern>\t--\tripgrep notes\n
        Remember to use #tags (for easier grepping)!\n\n'
    elif [ "$1" == "date" ]; then
        {
        echo ''
        echo '# '"$(date +"%m-%d-%Y-%T")"
        echo '-'
        } >> "$fpath"
    elif [ "$1" == "" ]; then
        less +G "$fpath"
    else
        {
            echo ''
            echo "$@"
            echo ''
        } >>"$fpath"
    fi

In short, writing $ notes prints out displays the notes and writing $ notes <text> appends a new line. This is extremely powerful because of it's simplicity and easy accessibility in terminal (where I spend most of the time anyway)

edit:: formatting edit2::

I very often keep this (with extended bash history) to keep notes about long commands I need to use later in the future, but not often. One had to do with imagemagick and resizing/compressing bunch of images in a directory. Added tags #imagemagick #command and in split of second I can get the command again whenever needed ;)