If you need DSP block and high speed with good price, then select Spartan3.
Elsif you need one FPGA to support 5V IO and simple Power supply, then select Spartan2.
Also you can try altera's Cyclone/2 and Lattice' XP/ECP2.
The most important thing is what are you designing now? And what is the key factor you need.
You know that Spartan-II was derived from Virtex and Spartan-III origniated in Virtex-II. So spartan-III has multipiler and memory array, also DCMs on Spartan-III has more capability compared to Spartan-II.