However, for quick access to the town, nothing beats sappers. Siege towers are way too slow (those guys take an eternity to climb the tower to fight, by the time they're done, the battle's over). Ladders can be faster, if they can sieze a gate without much resistance. This is usually not possible if the defenders have a decent-sized army (they will usually not oppose a single ladder team, but will defend a ladder team backed up by an assault force) I've avoided the ram-vs-gate approach or going through a gate opened by spy for fear of the oil, thus I don't know how bad it is to try to get in via a hostile gate (other than wooden wall cities that don't have oil).
my experience has been a bit different: if i use a number of seige towers from different directions and sappers simultaneously. the guys with the seige towers are usually on top of the walls first. given that they silence all the sections they occupy and then make them fire at the defenders: i think, it's a bonus.