Depends on what you are after - for me always buy on condition rather than mileage
Spec is important to alot of people so look for:
Service History
Xenon Lights
Highline Display
Multi Function Steering Wheel
18inch Monza's with decent tyres (indicates the car has been looked after if decent branded tyres are fitted rather than ditchfinders)
Armrest
RNS 510 Headunit - satnav and touchscreen
Leather - wingbacks if you can find them (rare) - check for drivers seat bolster wear
Folding mirrors (rare)
Rusty arches (common)
Check the mot history online to see what work has been done and for any outstanding advisories, also a free way of verifying mileage
Dont be put off by high mileage cars - as long as they have been maintained, mine is on 175k and tight as a drum
Good luck