Celeron 346 3.06GHz vs. Pentium D E2160 1.8GHz vs. Core 2 Duo 1.8Ghz

I am thinking of buying a Dell Optiplex 745 that offers 3 different processors. One is a Celeron that offers faster speed (3.06GHZ) vs. Pentium D or Intel Duo Core — both 1.8 Ghz.

Which one would be best for business applications?