Go with the Mercon ATF as recommended in your owners manual.
Most places I've found don't carry the Motorcraft Mercon; might be a good idea to order it online somewhere or specifically ask for it specifically (by part number) at your dealership. Will be worth the price IMO.
From our 2007 owners manual (pg 218)
Power steering fluid: Motorcraft MERCON ATF
Part Number: XT-2-QDX
2010 Ford Escape 3.0 V6
2004 F350 6.8L V10
1986 XR4Ti 2.3L Turbo
2007 ST ; formally bewst'd - R.I.P