Blanco intentionally aimed to give a more colloquial reading of Thucydides' sometimes "compressed, often crabbed syntax of the speeches." (p. xi). He felt that trying to give an overly literal translation of Thucydides would end up sounding ridiculous to modern ears. Victor Hanson (Who Killed Homer?) believes Blanco's estimation of his own work is too modest and believes he's actually made Thucydides more readable than Lattimore, who was aiming for the professoriate.

Crawley's translation was done in the late 19th century, but his English is not archaic. Unlike other translations done in this period (especially of the Church Fathers under the editorship of Philip Schaff), Crawley's reads very well for a modern. In my estimation, Crawley balances faithfulness to the text and readability in English the best. Plus it's nice that you can actually read it for free, since the copyright is long gone.

Strassler's version is just an updated version of Crawley's translation, not a new one itself. The real benefit to his version is all the maps. Yes, he has "updated" the English, but I've never found Crawley's translation to be difficult.