Bi-amping Rules

I wasn't sure if this question belongs in the amp or the speaker section but I figured I'll post it here. Those of you who have bi-amped your speakers, what's the general rule for deciding which amplifiers are better for low frequency vs. the high frequency drivers. I recognize an accurate answer will depend on the particular speakers and amp combinations but I'm looking for general rules of thumb from personal experiences and not application specific recommendations. For the sake of the argument, let's assume the amps are different but the gains on both amps can be adjusted if that matters. Thanks.