Diffrernce in age between them is only half a year (Radionova 06 Jan 1999, Lipnitskaia 05 Jun 1998).It's really early but it looks like we will see a big battle of Lipnitskaya and Radionova at junior worlds this year.
Radionova has more complex jumps, but Lipnitskaya has better PCS, better spins, better stability.
Radionova has progress, but Lipnitskaia also doesn't sit on her back, her jumps this season will be more complex.
At Junior Nationals (Feb 2012) Radionova had 178.94, Lipnitskaia 191.92.
Who will be better at new season - nobody knows.