A New Hope was great but it suffered from some plot holes, plot pacing issues, some special effects rushes, and just a general lack of polish. Empire was a professional effort with proper production, budget, director, an better emphasis on acting and character development, better scripting, Yoda, and, last but not least: Lando.
It was dark and deep and delved into the truth nature of the Force. It brought out emotions that the first movie could not. It has more creative planets and better dialogue.
I don't understand how A New Hope could be considered better other than the fact that it introduced the Star Wars universe.