Neil Lennon's CV will naturally look better as he has been a manager for 11 years in comparison to Gerrard's 3. Additionally, his managerial career has coincided with a period where Celtic have largely held a massive financial advantage over Rangers or Rangers were not in the same league. This, of course, is not the fault of Lennon, but is true nonetheless.
He has been emptied from 3 of his 4 managerial appointments and left his Celtic legacy in tatters. The simple question would be: if you were forced to appoint either manager tomorrow, who would it be, Lennon or Gerrard?