Well, here's how I would rank them, judging only by the tours Ive seen (was too young and oblivious in the 80's).
1. Zoo TV. What a huge show, nothing like this had ever been done before. Total sensory overload. Bono's falsetto never better. They were trying to be cool, and surprisingly they were!
2. Elevation Tour. Just the feeling upon hearing the first notes of the Elevation remix over the PA was worth the price of admission. What an uplifting feeling. (in my opinion their best opener).
Some would argue some of the new songs were a little bit slow, but they were just so well written and performed I couldnt help but love them live. Bono sounded great most nights.
3. Vertigo. band sounds awesome, Bono sounds great. My main beef is, the new songs just dont do much for me, and they dont really develop over the course of the tour (How can a song like Love and Peace really go anywhere new). Varied setlist was nice, altho they needed to play the new discotheque more! On the plus side, has Edge ever played better? Very close 3rd.
4. Popmart. Great stage design, but for me, not much else other than a few of the songs were awesome live (Mofo, Do You Feel Loved (why did they drop this), Miami, Please). Karaoke quite possibly the lowest entertainment moment of any u2 tour. Bono bottomed out many nights, his voice just wasnt there for much of the tour. Most static setlist ever, no surprises.