Here is a list of fan pairings that Sylphiel is commonly placed in both het and yuri. This is by no means a complete list; just the ones I like or dislike or have an opinion on. As the visitor you don't have to agree or disagree with me but please be mature about it; these are just my opinions afterall.
This is probably the couple that would be the best het pairing since Sylphiel has actual feelings for Gourry in the series and has made them quite clear. Although, both have quite contrasting personalities. Sylphiel is reserved and quiet, and Gourry is bouyant and full of life. There's not a huge fanbase for this pairing and it seems they're only paired up together in fanfiction as an excuse for Lina/Zel writers, thus there's not any focus on Sylphiel/Gourry.
I really happen to like this particular pairing for when my Xelloss/Amelia obsession strikes. Granted, I'm more of a Zel/Amelia fan, but this pairing does have some potential in its own right considering both are very introverted. I've seen a few fanfics but not a lot of fanart, which is a shame because I would like to see more of this pairing.
This pairing has a lot of potential even though the two have never met in the canon storyline. There's potential for conflict, especially if one writes the pairing before or during the TRY storyline. It would take some work though, since Sylphiel would have to deal with Valgarv's destructive behavior. So far, there's not much on fanfiction or fanart but I would love to see more of it since it's just sexy in its own right.
No! No! No! NO! Their personalities clash far too much for them to have that kind of relationship and while I like Sylphiel being with a dominant male, Xelloss would be too dominant for my liking. Though, I have seen some lovely fanart of the two together but most of it isn't romantic in nature.
I won't lie, I adore this pairing a lot. I'm tempted to write some of it myself but I don't know how good a job I'd be at it. This is my yuri OTP, mostly because I love the way both girls interact with one another and Lina is the one Sylphiel is closet to aside from Gourry. There's not much of the pairing out there to recommend to others though, which sucks because this is one of those, "There needs to be more!" pairings.
Another pairing that sparks my interest because there is so little out there for it. I've read perhaps two fanfics and seen one doujinshi where they were paired together. They would go well together, but both still have feelings for two guys in the series, so it would take a lot of hard work just to get around the Gourry and Zelgadiss factors. I'd read it though if someone showed me a good fic.
This pairing would be very cute, perhaps even a bit too cute. I can picture both of them drinking tea together and discussing ways on how to discipline Valgarv once he's hatched from his egg and starts getting into trouble. Haven't seen much of anything for this pairing though.