The singer - who came second in the 2010 series of the show - insisted that the programme would become "too serious" if there weren't any fun performers in the live finals.
"I remember at the time I was on the show, people gave Wagner a really hard time," Ferguson told Digital Spy. "I just loved him - he didn't bother me at all.
"People were like, 'It's about the music', and I was just like, 'He's having a ball!' He's up there dancing away and has all kinds of gorgeous girls around him and I was just like, 'He's having fun'.
"At the time when I was on the show, it didn't bother me at all," she added. "When you're watching The X Factor it's nice to have that entertainment factor.
"It's a Saturday night entertainment programme and it could get too serious if we didn't have bits of fun in it."
Ferguson also revealed that Jahmene Douglas, Lucy Spraggan and Ella Henderson are her early favourites, adding that Spraggan's original song 'Tea and Toast' made her cry.
Ferguson's repackaged edition of her debut album Heaven is out now and features her new single 'Backtrack'.
Watch the music video for Rebecca Ferguson's new single 'Backtrack' below: