The former N-Dubz singer also suggested that last year's winners Little Mix had pushed this year's groups to deliver in the early stages of the competition.
"The groups this year are great. I think after Little Mix winning last year it's made the Groups who have auditioned really up their game," Contostavlos said.
"There are also some great solo singers, but at this stage you can never tell who is going to go all the way to the live shows."
Contostavlos also revealed that she is still working with Little Mix as they prepare to release their debut album.
"I still see them and they still ask for my advice," she explained. I love those girls!
"I'm more of a behind-the-scenes advisor to them now, as they have their own team doing great things for them."
The X Factor returns for its ninth series on Saturday, August 18 on ITV1.
Watch the music video for 'Wings' by Little Mix below:
Photo gallery - X Factor 2012 - Behind the scenes:
Copyright: ITV Fremantle Media