It also depends on which generation of CPUs you're talking about. The previous generation i5s consisted of a few dual core models as well, like the i5 661 and the quad core models like i5 750, 760.Present Sandy Bridge i5s are quad core CPUs (I'm talking about desktops here).
When you say AMD dual core, it unclear which series you're talking about since there are a lot of dual core AMD CPUs.