Our democracy isn't perfect, but it's the only system, which is suitable for the USA.
USA isn't a democracy, it's a republic. The word "democracy" is not even mentioned in its constitution. I bet that most of US citizens have no idea about that simply because they have no time to read the constitution and its amendments.
http://www.whatwouldthefoundersthink.com/a-republic-if-you-can-keep-itIf democracy doesn't work, can one party system like communism be better?
Exactly like modern two-party system works in the US. It would be hard to deny that these two parties are merely a formality created to split the public opinion in order to make manipulations easier and cheaper. This approach isn't unique, a lot of regimes are acting this way. Regular members may even believe that their parties are real, but top officials of both parties are directly linked to each other and their agenda is amalgamated to the point of indistinguishability. Even if one of parties would disappeared tomorrow, the system will continue to work as if nothing happened.
However, it's neirher good nor evil, it's just how the system works. Especially if you remember that parties are not uniform.
There is no such thing as single-party system because party members don't share their brains. You may have it de jure, but it's merely an illusion. Each alive party has a set of factions with different agenda, sponsors and interests, which are effectively acting as different parties. Chinese Communist Party is not uniform, it has a moderate faction, liberal clowns and radical leftist idiots among its members. Same is correct for almost every political party in the world. Just compare Biden, Hillary and Sanders and you'll see the point.
Each party has a set of factions as well as opposition for them.
No, Soviet Union as the world's first nominally communist state proved its inefficiency.
You may be surprised, but joining the CPSU wasn't obligatory to run for office. In fact, councils of all levels had independent MPs and their share was ranging from 30 to 40 percent. Don't you think that these independents have acted like a second party? From the logical point of view, there is no difference between big party vs. independents and one big party vs. another big party. In fact, the second is even worse because elites of both parties may negotiate to form a unified agenda, effectively betraying their voters as the result.
The point is that number of parties is irrelevant. The only thing matters is a compromise between continuity and adaptability. If the system is balanced then everything will be fine, no matter how many parties are there. Shifting the balance to continuity will result with absence of changes, both "good" and "bad", leading to degradation and corruption on all levels of your state. As the result, its competitors will tear it apart. In opposite situation, shifting the balance to adaptability, the system will eventually destroy itself from within through the civil war or another violent scenario.