Rhys is a great name. I definitely prefer it to
Dylan.
Dylan is overused and is just nms. Out of the others, I like
Gavin (despite its popularity ) and
Owain.
Gareth is interesting, but the "th" sound at the end makes it sound off to me.
Taliesin would be a nice middle name. I don't think that I would use it as a first name due to pronunciation and spelling issues.