Well..I think Radar is a wrong choice to be the 4th single
it's not sucessful in many singles chart
like Billboard Hot 100, it's only #90 on that chart

many people many get bored of the Circus album's tracks
and maybe they've already bought the album
if you still release single from this album
i think the sales won't be good!
3 month for one single, it's too long!
but if u really want me to pick one track to be the next single
i would choose 'Unusual You'
it's different from the other Circus tracks
and britney usually have some fast songs to release as singles!

hmm..britney's next album will release in October
do u really think u have time to release the final single from Circus
and make a music video and promote in worldwide within one month?