I think Barkley may turn out to be better than Sigurdsson but at this moment in time he isn't, its close though.
They are also slightly different types of players.
Barkley is more of an explosive and exciting player whereas Sigurdsson is more efficient and clinical.
I would love to find a way of fitting them both into our team but it would leave us very narrow assuming we would continue with 2 more defensive midfielders behind them from Gueye, Barry, Schneiderlin and Davies.
I'm not sure the number 10 role is our most important void to fill, Barkley is showing to be more than capable at the moment.