I use to always use just sapping, but that was with mostly cavalry armies (with mercenaries to handle the saps). Infantry is too slow getting through the holes, and will get shot up by the towers.

Plus, in my Thrace game, I found the computer was pretty stupid about choosing the sap points. Put them on opposite walls of a corner tower. So once the walls went down, the tower was impossible to capture, as you couldn't get there (and no "door", as it was a corner). I decided to reload that one, as there was no way I could get my army through without taking heavy losses. If I get stuck with that situation again, I'll use the siege tower first, and do the saps after.

Bh