I am going with Aeriseph mainly out of preference.Zerith is rightfully still canon but there is just something so drawing to this what could have been pairing.Plus I always felt that Aerith and Sephiroth who were opposing forces should have had a more personal relationship to make their contrasting nature even more noticeable.I kinda of wondered if the developers could have had Zerith still be canon but Sephiroth knew who Aerith was before he went insane and then secretly developed feelings for her but kept it hidden out of respect for her relationship with Zack.
But then again people just like the pairing in a fanon way.Its actually has a big fanbase that has developed over the years.When most people ship Aerith and Sephiroth its when he was sane mainly because people pefer him ironically being good than being bad.
I know there a lot of bad fanfictins about Aeriseph but the good ones that keep them in character tend to be well written and are really a treat to read.