The prince-electors of the HRE were those princes who, initially when the Empire was formed, selected who would be crowned the Emperor. Though this position became more ceremonial once the Hapsburgs took power, they still wielded power and prestige. The composition remained largely static over the years:
3 ecclesiastic prince-archbishops (Trier, Cologne, and Mainz) and 4 secular princes (Bohemia, Electoral Palatinate, Saxony, and Brandenburg). Two later additions would be Bavaria and Hanover, the former due to the Wittelsbach branches of Bavaria and the Palatinate conflicting with one another and the latter due to balancing between Protestant and Catholic electors. The title became meaningless once the HRE was dismantled under Napoleon.
What if, when the Empire was first created, there were more electors or different princes were chosen? Who would have been picked? How might this affect who the Emperor was? Would it have made it more difficult for a single dynasty like the Hapsburgs to claim the title?