What do you think would have happened had Vitellius not rebelled, or had rebelled but had not had two so capable and unscrupulous generals as Caecina and Valens ? After the assasination of Galba, Otho had firm loyalty from the Praetorians, and the Legionaries in Dalmatia, Pannonia, Moesia, Syria, Judea(Vespasian), Egypt and Africa, and at least in the beginning of his very short reign, those of Narbones Gaul, Aquitania and Hispania Tarraconensis as well, and was of course conferred all titles and powers of Emperor by the cowered senate. Had he had decent generals in command (his war councils to me have a similarity to those of Pompey in that Civil War) and had managed to put down Vitellius' officers rebelion - would he have made a go of being Emperor ?
When you say Otho and Vitellius were rejected - who do you mean they were rejected by ? The soldiers ? Offficers ?