I think you may be confused with the technologies?
Dual-core processors are a general name for all, well, dual core processors made by Intel and AMD, both. The Intel lines are the Core 2 Duo, the Xeon [These are primarily used for workstations], and the Pentium D. For AMD they are the X2 series, and the FX series [for now].
If you mean, dual processors, are you talking about, something like the Socket F processors from AMD where you have to buy two of them? [Their quad-cores].
From Intel, the line in order of least powerful, to most powerful is like this:
Pentium D
Xeon [Workstations, mainly.]
Core 2 Duo.
Those are the dual-cores. If you're talking about Quad cores also, the quads would be at the end of the list. The Core 2 duo's and the Core 2 quad's are for home use. They are relatively cheap, and excellent for gaming/video/sound editing, and should fit the use for most people's needs today, unless you definately need top of the line. In that case, you should find yourself looking at the Core 2 Quad's [Q6600, Q6800], from Intel, or, if you're stuck with getting AMD, their Socket F processors, however, these aren't the best in town.