[3.P] Binding outsiders to your service

[ImperatorK]

Let us assume that PC is neutral and some kind of caster. I want to bind to my service at least 2 outsiders, a succubus and an erinyes. Is Planar Binding the fastest way to do this?
If yes then how can I do it with minimum risk and cost? Not totally minimum, mind you, just so it is reasonable and worth it.
If there is a better way, then what is it?

[peacenlove]

Demons and Devils value strength. If you treat them like an equal you lost the game.
Give them assignments that are suitable to their alignment.
Planar Ally is the safest since you bargain with the outsider and he would be one that is servant to your god/philosophy.
Planar Binding is more dangerous, because you need a hefty amount of charisma to woo the outsider to your service.
Simultaneously binding a lawful and a chaotic outsider is a recipe for trouble, especially since erinyes are described as vengeful fallen angels.

[Urpriest]

Dig up the Malconvoker handbook. Even without a great Charisma you can stack up a bunch of check penalties and the like to force a Succubus to serve you. Takes a bunch of spells, but it's not actually risky.

[Psyren]

Yeah, the trick I saw was to Geas her to drink a glass of water outside the circle or something, then come back when her stats are in the single digits and get her true name from her.