Capitalist citizens tend to do better because their private organizations & government are willing to oppress the people in other parts of the world in order to extract their wealth. Communists respect the lives of poor people and refuse to take advantage of that, or oppress them further.

If a capitalist nation is completely cut off from the rest of the world they become fascist very quickly (Germany, middle east, etc. etc.), when a communist nation is cut off from the rest of the world they become poor (Cuba, USSR, East Germany, etc. etc.).

I don't think the argument of "I'm rich therefore I'm better than you" is really a strong one.

When all else is equal, life is better under communism for the vast majority of people, just not the wealthy people of capitalist nations. But even for the capitalist "middle class", when it comes to the essentials (Food, water, housing, healthcare, equality among women, minorities, etc.), communists still beat capitalists.