The M19 has a classic Altec alignment, peaking around 50 Hz with the -8B, and requires the room to fill in the rest if need be, while the Onken peaks lower based on a percentage of its (Fs/Qts) spec to help the driver above Fs where it runs out of excursion, but rolls off at a steeper rate, so it just depends on the room, speaker location and how much bottom end you need.

GM