Interesting topic. From my point of view the main criteria when discussing about clubs of European pedigree should be Prolonged success on the fieldA world wide fan baseA large domestic fan baseConsistently large attendance figuresCriteria like academy success * and the ability to attract players and sponsors aren't as important to me because they are largely dependent on extremely fluctuating factors like a team's wealth, public recognition, pull in the media or even its luck. *Ajax deserves special recognition for what they've been doing in the last decades is IMHO an exception. Now when it comes to small leagues in countries where football has never really developed properly and European success is little more than a dream the only criteria that matter are : Prolonged success on the fieldSize of the domestic fanbaseConsistently large attendance figuresSo in Greece's case the top clubs would be Olympiakos, Panathinaikos and AEK (in that order). All three are based in or near Athens, have never been relegated and have won 69 out of 75 league titles. However the football in this county is as corrupted (if not more) as the society and the top clubs are amongst the worst offenders. It wouldn't be far-fetched to claim that Italy's Calciopoli is a childs lie in comparison to what has been going on here since 1996, the BIG clubs (namely Olympiacos) have gone from controlling the referrery committee and planning who gets the league and who gets relegated to literally owning more than half of the teams in the top division. That usually leads to the small clubs getting bankrupt and the big ones getting bitch-slapped whenever they play a game which they have no power on (ie Europa League/Champions League).