Answer to first question is yes, and the second one is difficult to answer because it is rather unclear: What do you mean by INT? Schengen countries such as Norway are handled in the same part of the airport as domestic flights. As for the Schengen -> Non-Schengen transfer, no big deal in any Greek airport, just show your passport at the immigration booth and that's it. Finally, there is no such thing as "other factors being equal": You have to consider a) the connection time, b) the flights (e.g. time of the day and c) the price. Then you simply decide.