I always felt that The Empire Strikes Back has a pretty slow middle. The bits with Luke and Yoda just weren't that engaging to me. If anything, I felt ever so slightly bored. Also it does sort of end on a cliffhanger (which is to be expected for a middle entry).

I went with A New Hope. I only saw Star Wars for the first time last year, and it didn't seem dated. In fact, I really enjoyed it.