Code Review Matter CRM 2011

What's your opinion, if your queryexpression or querybyattribute have a columnset constructor call like this columnSet.Columns = new ColumnSet(false);

Is it recommended, especially if you just want to check if one record exist?

Which is the best code

1. columnSet.Columns = new ColumnSet(false);

2. Retrieve only the target entity unique id. e.g columnSet.Columns = new ColumnSet("contactid");

3. No columnset declaration.