I've really grown accustomed to Center and S-1 for spreading the audio. I find center to work great for instruments and overall and less so on an group vocal bus. When using s-1 or micro shift im bussing to it seperately and its generally is go to for vocals or instruments. The Izotope Ozone 10 spread seems to be the best on high end but i always wonder about it's capacity to maintain fidelity on a bus level and not just the master bus.
Also, something else i think about is is there phasing that occurs if the stereo imager is after the eq low and hi cut? should that finishing eq in mastering be done directly after the stereo imager or before?