If Can't Be Tamed actually got a second US single, maybe it would've pushed gold. HWR weren't behind the era at all, considering that they didn't fund a cent to the CBT music video and Miley had to pay for the entire thing with her own money.

Unbroken got 2 singles, with Selena getting 3 from their last respective eras, and their album sales are nothing to write home about. Let's keep it low on the shade.
Demi will have the most single success next era if Miley doesn't deliver hard.
Selena will have the most album success because she's consistent.
Miley will have the most tour success, no argument needed.