If you will be running more than one application at the same time I would recommend buying a processor with more than one core, since a processor with 2 cores will be abel to process 2 thread of information at the exact same time.
Howerver if you will be running only one application at the same time, then you might want to have a processor with only core but higher clock speed.
So basicaly it will depend on your own processor needes.
If you need more buying recommendations I would suggest contacting an Authorized Intel(R) Distributor.
You can find a list of Authorized Intel(R) Distributors at: