Horned Devil

Not to be confused with these.

I'm not sure where to start here. Great stats all around, high AC, Large size, four natural weapons, fly speed... what's not to love?

The special abilities range from decent to excellent. Infernal Wound and Fear Aura are so-so, but Stun adds a strength-based save-or-lose to most of your attacks (having to use a spiked chain isn't much of a drawback). Regeneration, as has been said before, makes it nearly impossible to kill you through damage: how often are monsters carrying good-aligned silver weapons?

All this is without getting into the spell-like abilities. Dispel Good and Chaos are decent if you're fighting such creatures (which, given you're a devil, is probably often). The same goes for Magic Circle Against Good. Greater Teleport is still useful (though less so with other party members having access too), and Persistent Image is the next step up from earlier illusions. Fireball and Lightning Bolt, though... I'd pretend you don't have them.

It should be clear that a horned devil is a more-than-capable monster that can serve both as ubercharger and tripper. +2 LA is probably the best option here, but I'm slightly inclined towards +3 as well.