Newey keeps F1 world on hold: What are currently his logical destinations?

With the recent signing of Ferrari's Enrico Cardile as Chief Technical Officer, Aston Martin bolstered their key staff. With the Italian on board, the British team's technical staff's strength has increased. The coming months will surely reveal whether Adrian Newey joins Aston Martin as well, or whether he will respond to the advances of Ferrari, Williams or perhaps an outsider like McLaren or even Mercedes. Which team currently holds the best cards for the designer departing from Red Bull Racing?