Neil Tennant and Chris Lowe also suggested to Digital Spy that GaGa may have competition from Rihanna at present for the title of biggest popstar.
"GaGa's going to produce a really good greatest hits album in about two years' time, isn't she?" Tennant said.
"It's going to be absolutely fantastic. And in many ways, that's the best achievement of all in pop music. To have an excellent greatest hits album."
The duo have worked with Kanye West engineer Andrew Dawson on new album Elysium and praised the rapper's last two albums for sounding different to other hip-hop.
"Also - daring to sing - he can't really sing, putting it through the Melodyne, Auto-Tune or whatever. It sort of really works," Tennant said.
"You kind of have to accept that. People still criticise it, because it's such an overpowering sound in modern pop music. There are still people who call it 'The Cher Effect'."
He added: "It's always interesting in pop music. Something comes along and it's treated as a gimmick.
"If it's any good it just becomes part of the repertoire, and then of course gets taken to the ultimate extreme. And now it's on so many records."
Listen to the Pet Shop Boys Elysium album sampler below: