I'm extremely pleased that Radar was chosen. It's my second favorite on the album, and in my opinion I think it should it was the best decision.
Although, I feel that Kill The Lights should have been the fourth, since that seems to be the most popular behind Circus, If U Seek Amy, and Womanizer. However, when I viewed the Circus album on iTunes, Shattered Glass was the fourth most bought out of the 13 on the album. Radar and Unusual You were holding 5th. Kill The Lights, Out From Under, Mannequin and Lace And Leather all holding 6th. With Mmm Papi, Blur and My Baby standing in last.
If iTunes buyers voted on the next single, Shattered Glass would be the fourth. But if I myself could choose the next single, I would have chosen Radar. Which is I'm highly satisfied with this decision. :D