Welcome to the forum.
It depends on what you want the car for: if it is for doing the regular school/supermarket run then don't bother - they thrive on longer journeys where they get to the proper operating temperature. If it is for towing a trailer then they have a good reputation for this, at a reasonable price. Buy the latest one you can and from a Vauxhall dealer/Network Q if possible. The post-facelift models (i.e. after about 2013) appear to have had earlier problems addressed by the manufacturer, but be prepared for general ignorance on the part of the dealer - there doesn't seem to be many Antara experts about with regard to either sales knowledge or mechanical experience. Some of us have found direct contact with Vauxhall UK to be the best source of information. Beware of what previous owner(s) might have done to the engine and exhaust system through their short-term driving habits; if the DPF has been ignored then trouble will be brewing. As Swinton says, there are instances of transfer box failure on 4WD models (as with BMW, Land Rover, Kia, etc) but the reasons for this are not clear. The SE Nav model has most of the gizmos that people want these days and for a vehicle with a 2.2 diesel engine and weighing two tonne I am pleased with mine, returning about 35mpg average. If you get one, I suggest you stick with a Vauxhall dealer for servicing and repairs (join the VX Service Club) because they at least have access to the manufacturer in the event of a query. A recent one in good condition will represent excellent value if you are a buyer, but not if you are a seller, so you will possibly get best value by keeping it for a few years and following the maintenance recommendations by the book. Good Luck.
2015 2.2 CDTi SENav 163ps manual 4x4 in Carbon Flash with 19\" alloy spare towing a Bailey Unicorn III Madrid @ 1500kg.