This should have been a poll and should have excluded primary donate (tech) rigs. Interesting some of the comments are. I was taught air supply right (including the snorkel if used) and everything else (BC, spg, drysuit) left. I tend to be anti-personal preference and consider what is standard. But obviously standard is not standard the world over
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FWIW, I dive both traditional right side octopus rigs and long hose primary donate rigs. Which I choose depends upon circumstance and in particular if my wife is buddy diving with me. I once tried to move her to long hose and primary donate (which this thread is not about) and after a bit of fussing and arguing she told me to leave her alone and gave me that look!
And further off course for this thread, when solo (and I am SDI Advanced Diver Solo) I do not have a "long" hose nor an octopus or any of that, just one second stage on my (single tank rig) back gas and another complete regulator, slung let side for my redundant supply. But, I suppose if an errant diver where to swim through my solo universe and present me with the issue of their being OOA, I would provide them my left side (pony/aux) regulator so in that case I do have an octopus and my octopus is indeed left side.
James