While I have had my differences with Peter337 in his present and previous incarnations, this time it is hard not to think he was screwed by an examiner who was a total w@nker.
With respect to an alternate airport there is no grey area. If the airport has the appropriate weather forecast, no notams which affect its suitability and is within the fuel range then it is a legal alternate. The examiner may not like your choice but it would seem to me the examiner is grossly exceeding his authority if he were to mark you down for presenting a legal alternate not of his liking.
As for selecting an alternate outside the make believe fantasy land that is flight school IFR training in pretty much every country, well that is a different story.
When flying IFR privately I use the same criteria as when flying commercially. There will be 3 alternates
1) The commercial one: That is the place that will cause the least cost and inconvenience
2) The legal one: That is what goes on the flight plan and meets all the legal requirements
3) The inflight decision one: This is a result of the constant assessment of how things are going and where to go with the worst case scenario and will be updated with the a succession of "near to me" airports as the flight progresses.
Some days all three are the same, most days 1 and 2 are the same and the odd day 3 is the only one that matters.