if its luxury you want go to http://www.buenosairesstay.com . ... it was a very good rental experience and they speak english which made everything a lot easier
goodluck!
you should check out the big grocery store on Mendoza somewhere between the china town and Libertador... they have great fish and supplies to make your own sushi! at least this way you´ll know maaas o menos where your ¨raw¨ food is coming from!