Romanos IV Diogenes as worst?! Why? because he tried to restore a dream while he was betrayed from all the sides and finally lost a regional battle which cost him his life ? No, he was an original Byzantine emperor who made the best for his empire, such a wronged personality and judged by history whith cruelty... For me , he was the most "human" emperor and whenever i think about his reign , i get emotional...
as for the best...
1.Basil II
2.Heraclius
3.Ioannes II Komnenos
4.Justinianus
5.Constantinus I
6.Julianus
worst: 1.Phocas
2.Irene the Athenean(which was half a Chazar if i'm not mistaken...)
3.Aggelidian dynasty(all this handycapped ganc which <<<<ruled>>>> the Byzantine empire until 1204)
4. Theodora(whith or whithout partner)
5. John V palaeologos (i could peek a lot from the Palaeologian dynasty but i choose him, as the last step to downfall)