Don't take too much notice of who has deeply researched the company - they should be familiar with it but it's not very important - they will learn more if they get the job. You need to get an idea of the person, not their research skills (unless you're looking for a researcher !).
Look at what they say when they're NOT singing their own praises - you might be so impressed with their positive outlook, high motivation and great organisational skills that you miss borderline psychotic.
If you're interviewing for someone you will be working with, picking someone you feel comfortable with is NOT inappropriate - it should ensure a smooth working relationship.
Avoid people that speak corporate BS.
Have someone greeting the applicants - they should chat to them, make them a coffee, relax them and show that it's a good place to work. After the interviews, compare notes with the greeter to see if you agree. Some people are different in the formal interview.