all depends what you're after. a hot Xf is alot of fun. a stock zetec is dull... (await hurled abuse from other owners). a hot zetec is a much better bet, fit cams alone to one and things improve lots.
The zetec is the more driveable carbs or no. handling is slightly better with the xf I would say but there's not much in it. If you want to go faster and have an upgrade path to 220 and beyond then there's not much choice. might also be wortht considering duratec though if power's the goal. i do kind of miss the xf noise and gutteral bark. i don't miss the regular oil checks, carb balancing, poor fuel consumption and general feeling it may let go before long though.
Nigel Mills - 2.0 zetec