Thureophoroi are far better in my opinion. They are perfect to outflank the enemy while your phalanx are holding the lines, if you lack the cavalry, or for defending your own flanks. I usually hide them a bit behind my phalanx, and enable fire at will. After all missiles have been launched I usually outflank the enemy with Thureophoroi together with cavalry. Few enemies survived that strategy early on on VH/VH. At least, the ones with a rather static kind of warfare.

Of course, such strategy will work far better once you get the stronger Thureophoroi - the Thorakitai.