I think this is a problem with MPV and not with the gas. On my ES 02 I was having the same problem with bad smell like other owners. Initially, (first 600 miles) was really bad. Then it went away. Now, I made almost 10,000 miles and I used all kind of gas in US and Canada. Sunoco seems to be the best. But, nevertheless, from time to time I can get a sniff of HS2 but never inside the van anymore. I have to emphasize that I use the same gas on my 2001, Acura TL. I used the same gas on 1999 VW Passat and I have never experienced H2S wonderful scent. Mazda engineers should design their cars so they run fine on most fuels not just selected ones.
Overall the van is excellent. Superior handling, comfort, and performance. Only problem so far I have had is leaking fog light - replaced under warranty.