Q:

Multiple influences over an undead, who controls it?

There are many ways to gain control of a mindless (or even intelligent) undead, but none of the methods indicate what happens when more than one have influence over it. 
Lets take a good and evil cleric. The evil cleric has created an undead and has influence over it from this. The good cleric then exerts their influence over the undead. Who has control in this case? Does the source matter? Lets make it even more complicated now and a friend of the good cleric walks in, an arcane spell caster who also casts a spell to influence the undead. Now who has control? 
Possible methods of control or influence are:

Control Undead spell
Command Undead spell
Command Undead feat
Animate Dead spell
Command Undead Death Sphere Talent - Spheres of Power

A:

Its decided over opposed Charisma checks
The answer is on the Magic chapter, under Stacking Effects:

Multiple Mental Control Effects
Sometimes magical effects that establish mental control render each other irrelevant, such as spells that remove the subject’s ability to act. Mental controls that don’t remove the recipient’s ability to act usually do not interfere with each other. If a creature is under the mental control of two or more creatures, it tends to obey each to the best of its ability, and to the extent of the control each effect allows. If the controlled creature receives conflicting orders simultaneously, the competing controllers must make opposed Charisma checks to determine which one the creature obeys.

Note, however, that both are controlling the creature. The check only happens when they receive conflicting orders ("Go right" vs "Go left"). If they receive different orders, the creature will try it's best (most likely for intelligent creatures) to obey both orders.

