Without a doubt I would say Sarah Jane.
Something magical happened in his first 2 seasons, the elements were, well, just right. The combination of Lis & Tom with Philip Hincliffe as Producer, the stories etc. The alignment, let's say, was perfect.
The chemistry was definately there too, you believed they were best of friends. The magnificence of Tom mixed with the pure, strong hearted beauty of Lis.
Magic, pure beautiful magic. aaahh