You're not comparing video cards here. Optimus is nVidia's term for switching between two graphics cards (usually a discrete card and an integrated adapter), while AMD Radeon (assuming you made a typo in the original message and meant otherwise) is a series of video cards made by AMD.
As for what's better between nVidia and AMD, what are you looking at doing with your computer?
nvidia optimus vs amd redon..
which one better....
Like cklaubur said, you are comparing different things. Optimus is Nvidia's cut cost solution to pairing up a discrete card in a PC. The equivalent technology for AMD is Enduro.
Optimus/Enduro doesn't have dedicated electrical connections to a monitor or outputs, so it works by copying rendered frames directly to the integrated GPU's frame buffer, which is then displayed on the monitor. In that sense, it is a LOT like the earlier 3DFX Voodoo accelerators, or the PowerVR cards (not exactly the same, but idea is similar).
What you want to compare is EXACT models of the cards. Each brand (AMD/Nvidia) has SEVERAL tiers of performance, so once you choose a price category, you set the tier (more or less) and then you choose the best model depending on your needs.