I binge watched all seven series a few months ago. I think my favourite was the one when she was in Metro Vice. My least when she was in Manchester investigating drug gangs and taking on Steven Mackintosh's "The Street". I liked the way Tennison's relationship with Otley (Tom Bell) changed over time. Top telly.
Lately, I've been watching all four series of the Danish Borgen, so politics not crime, but I think Sidse Babett Knudsen, who plays Birgitte Nyborg, has the same kind of screen presence as Helen Mirren playing Jane Tennison. Maybe it's to do with a women in a senior role succeeding by sheer hard work and determination in a predominantly male environment. Also highly recommended.