HW and shield Saurus give you 17% fewer casualties suffered relative to spear Saurus in all rounds. They also cost about 9% less to field on the table.
Spear Saurus give you 25% more casualties inflicted in rounds where you aren't charging and can maintain three ranks. That's a 1% advantage in favor of handweapons even if they got to use their extra rank of attacks every round.
Overall this tilts things in favor of hand weapons, but not by much, if you chooe to field spear Saurus, it shouldn't cost you any games unless:
-you are fielding very small blocks of Saurus
-the scenario you are playing involves mostly assaulting or defending buildings
-You are playing a static army that is almost guaranteed to force you to charge them rather than attempting to charge you.
The following make spears more viable (though they don't make spearmen the OBVIOUS choice)
-Your general plan involves very deep ranks of Saurus
-You are taking Lore of Shadow, either Mindrazor or the Withering will make your every attack count (Lore of Metal has similar buffs and hexes but that help the same general way but are generally weaker)
-You are taking Lore of Light, Speed of Light means your attacks are worth more and the defensive buffs make up for your lack fo a parry save.
-You are playing a very fast army that is highly likely to get the charge on you
-You want to field the bare minimum Core and the extra points for spears will push you to 25%