Empire.

I love the atypical story structure. It starts up very calmly with a sense of security, followed by the discovery of the rebel base and by the exciting Battle of Hoth. After that the story splits into two very contrasting parts and then perfectly switches between the two; the fast-paced thrilling chase for Millennium Falcon, and the calm training on Dagobah. Finally, it converges into the tense finale at Cloud City with the shocking ending. I think this kind of storyline was quite revolutionary for a mainstream film at the time and this aspect is often overlooked when it comes to Empire. I believe this is one of the best cases of Lucas’ great story-telling ability.

I also love the fact that the storyline invests a lot of time in Empire and its secondary characters. I have always liked the characterisation of imperial officers (Piett, Veers and Ozzel) and the attention given to the imperial fleet and its ships. When I was a kid I was a WW2 naval history enthusiast, therefore Empire was naturally my favourite.

Above all, the acting and actor direction is in my opinion somewhat better than in Star Wars and Jedi.

If I had to pick a close-second, it would be Jedi. Maybe because it wraps up the Empire story really well. But in the end, all three are excellent films, forming a great trilogy.