Hazrat Ali's was simply the pehla Imam.
Now some say that Hazrat Abu Bakr, Umar and Utheman were much better companions then Hazrat ALi.
Well, for this reason they became the 1st 3 Khilafas. Now Khilafat is defined as Rule over Muslim Empire at that Time.
However Imamat is Rule over the whole kai nat...
Tu phir batao meri Musalman bahano aur bhaio.... Hazrat ALi ki importance ki gawayi (testimony) kyu mang ni ki zarurat par te hai.