This is an easy one for me. My favorite TARDIS interior is definitely the most recent one.
I love the metallic color scheme and the little circles of blue lights. I love the geometric design. I especially love the turn-y things with Gallifreyan writing.
At the time, I really liked the 10th and 11th Doctor’s TARDIS designs, but looking back now they seem so cluttered. There’s just too much going on.
I found this site when I was looking for pictures: http://www.thedoctorwhosite.co.uk/tardis/interior/
It’s a great reference for all the different styles and has pictures of the console, other rooms, etc.
The latest “desktop” is my favorite!