Thanks, Mini and Dolly. As several people have already commented, all three versions are acceptable. Speaking purely about preference, to me Argentine does sound more elegant when describing a person, 'an Argentine', or as a more sweeping adjective, e.g. 'the Argentine condition', however when describing everyday things I find it can sound a little pretentious or old-fashioned. e.g. 'My Argentine apartment', 'an Argentine friend of mine', or 'that Argentine beer we had last night'. But that's just me.