Marseille and AEK only. Its hard to answer 'best stadium' as many factors. Stade Velodrome is more iconic, visually stunning and bloody enormous. Only Wembley and Old Trafford are bigger in England I think.
Overall much prefered the full Athens away day experience. Athens miles nicer than Marseille imho.
AEK stadium newer, they're super proud of it and walking to the stadium and just around the immediate outside of OPAP with the bars was really nice and chilled with friendly fans, compared to being herded on busses into underground car park in Marseille.
Atmosphere in stadium and acoustics etc, Marseille easily wins. Better than anything I've ever experienced.