[gasparch]

Evernote. It proved so far to be the most useful. Especially because you can easily add tags to the notes.

When using 'clip to Evernote' browser extensions to add research materials you add same tags and then you have nicely linked together idea + research material.

I used to use index cards for storing ideas, but if you move often or just away from them - they are not so useful.

Hassle of digitizing notes are compensated by better availability.

For quick notes on a move I may use voice memo or voice note and then type in when I'm at the computer.