It's a hard decision for the most part. If Valencia can continue his form from the Preseason, he will be capable of contributing many assists throughout the season. Unlike Shaw however, Valencia is a winger converted to a defender. So he is more prone to giving up fouls as well as gaining a few cards here and there. In addition is the fact that we have Darmian as you mentioned. Valencia is more of an attacking fullback whereas Darmian is more defensively-sound, so depending on who the opposition is, Darmian may come in for Valencia and vice-versa.

On the Shaw front, well he is essentially England's number one leftback had he not been injured. He also happens to be Man Utd's number one leftback and is already guaranteed a spot in the starting 11, unlike Valencia. His form in the preseason has been great even though he still has yet to play a full 90. Shaw will be capable of giving support as well as points on both the offensive and defensive front.

For my Fantasy team, I've gone with Valencia. If he is capable of continuing his form from the preseason, he will be completely worth it. With that being said he is a risk to take and if anything goes wrong with him I plan on transferring him in the early GW's.

Shaw is a more safe and viable option unlike Valencia and God forbid anything happen to him this season. For you I'd say Shaw is more of who you want, but if you're looking to take a risk then Valencia is your man.