I've seen dual core i7 laptops
But if we're talking desktop:
i3 > core2duo
i3 > or = or < core2quad (depending on model and generation)
i5 > i3
Quad core i5 > Dual core i5
i7 > i5
More cores is always better than hyper threading (ie. quad core is better than dual core hyper threading) but this may not apply to Bulldozer when it comes out.
And as ps3hacker12 said, a newer generation CPU is generally better than older generation.
Oh and who the hell uses the term Centrino duo, seriously? This is 2011...