How to compare testudo formation vs phalanx? Which is better?
The Roman testudo formation was used solely to protest soldiers from missiles and arrows and was never used in hand to hand fighting, whilst the phalanx was the standard formation of Hellenistic armies and was designed to create a cohesive unit of soldiers who were far more difficult to push back or fight against that individual soldiers.
It is impossible to compare these formations as they were used for different functions. In withstanding missile fire, the testudo formation would most certainly be more effective, but in melee combat the phalanx would be considerably more advantageous.