Best = They asked me to collaborate with them and help solve an issue in their current test env. I got the job. When you already know someone is qualified, you want to see if they can work well with the team.
Worst = 5 hours of interviews, and then they gave me an hour to write an essay. 
An essay… ask me to write code ! An hour in, I knew I didn’t want the job, I should have walked.
The best was when I was interviewed for a Senior Tester role a number of years ago and had to draft a test plan and some cases for a complex workflow.
I drafted it all out, pointed out a flaw in the process and was offered a Lead role on the basis of my approach, at around £6k more.
Being able to demonstrate what I would do to test something paid dividends.
Worst was a Government agency, made me wait in an adjoining room, called me in late asked damn fool questions, and then ran out of time so didnt let me ask anything. They then insulted me with a low ball offer - needless to say I declined, much more politely than I felt like doing!
Most odd conversation in an interview - a Senior tester interviewing me told me she had fallen out of her loft and broken her arm. Very random, and I still remind her every now and then! 