All of them are kind of hard names to hear, if that makes sense.
Of all of them, I like Guinevere, but its very very olde English (Welsh). I'd be inclined to go for a more modern Gwen or Gwyneth. Both lovely names and much easier to grow up with and live with. Both are still from Welsh origins. Although saying that Epona is from Latin but tbh it doesn't roll off the tongue well at all.
Maybe one of them would fit as a middle name if you could agree on a first name?