Both of the two tools can help you do research on collocations, and WST4.0 can provide more statistical measures than AntConc, for AntConc only has MI and T-value statistical measures, but WST4.0 has five measures.
AntConc is free of charge. WordSmith Tool is commercial software. Antconc is capable of doing many tasks.
Both of the two tools can help you do research on collocations, and WST4.0 can provide more statistical measures than AntConc, for AntConc only has MI and T-value statistical measures, but WST4.0 has five measures.