Had an interesting interview where I had 4 panel interviews of 2-4 people in each time slot (13 in total) . My process is to write thank you notes on the flght home however many of the panelists really didn't say much. The whole middle sentence that looks to personalize the note becomes cumbersome when there was nothing memerable about the interviewer. I don't want to not include them of course as that could be a big backfire. I had thought about just sending a thank you note to the hiring manager and leave it at that.
(name redacted as I've turned on too many people at my current company to manager tools ;)