Think about your speakers and your listening preferences.
With identical amps you can do it either way.
I bi-amp ESL Hybrids and the best way for me is horizontal. That way I have better control over the separation between bass and mid/high. If you horizontally bi-amp you also need to think about passive versus active, which is a whole other discussion.
Experiment and listen - always the best way to make decisions, anything else is somebody's opinion and only yours really counts.
With identical amps you can do it either way.
I bi-amp ESL Hybrids and the best way for me is horizontal. That way I have better control over the separation between bass and mid/high. If you horizontally bi-amp you also need to think about passive versus active, which is a whole other discussion.
Experiment and listen - always the best way to make decisions, anything else is somebody's opinion and only yours really counts.