Party:
European > Mixed = Islam > Chinese
Solo:
Chinese > Islam > European
E.G.:
Overall, European = Chinese = Islam. A.K.A. Balance

Elaborate:
If Chinese is the best at solo play overall and the worst at party play overall, then they're in the Middle ground Overall.
If European are the worst at solo overall and The best at party over all, then they're in the Middle ground Overall.
Therefore, Chinese = European. (here is where Islam complicates matters)
Islam is speculated, based on information laid ALL OVER the net, to be able to solo decently without much hindrance and be able to party well without ruining the potential efficiency of the party.
Now here is a illustration to explain matters: Imagine a rating, 1 being the lowest possible 3 being the highest. Then take the averages to get the overall balance, afterwards substitute the number in overall for the civilization corresponding with that overall category.
1--------2--------3
European:
[1]Solo
[3]Party
[2]Overall
Chinese:
[3]Solo
[1]Party
[2]Overall
Islam:
[2]Solo
[2]Party
[2]Overall
Overall:
so: [2]=[2]=[2]
Substitution: European = Islam = Chinese
Party: [3]>[2]>[1]
Substitution: European > Mixed=Islam > Chinese
Solo: [1]<[2]<[3]
Substitution: European < Islam < Chinese
So conclusion, Joymax planned the game well:
If you prefer party play, go European.
If you prefer solo play, go Chinese.
If you Like doing both every now and then, go Islamic.