What is the more used planar inductor simulator? I have heard about m-a-g-n-e-t, s-o-n-n-e-t , asitic, fasthenry but not all of them are designed to simulate CMOS structures.
Regarding to my experience , the most stable and almost accurate simulator for 2.5D planar structures is Momentum of ADS.
Simulation results and measurements are meet in our expectations...
But for the others, some guys say good things..like Sonnet,IE3D , so on..