Top 5. Because there are too many romanization methods and they all suck.
Perhaps that's too harsh, but it is true that there are too many of them, and most of them were designed either by committee or by linguists, or -- even worse -- by a committee of linguists. It is, of course, a very tricky task to devise a romanization method; some are better than others, but all involve plenty of counterintuitive spellings.

原因五：（羅馬式）拼音方案太多且都讓人精疲力盡。
也許聽起來有些刺耳，但漢語的拼音方案確實太多，而大多數(shù)的拼音方案不是什么文字委員會提倡的，就是語言學(xué)家提出來的，更糟糕的是由那些語言學(xué)家組成的文字委員會提出來的。當(dāng)然，要發(fā)明一種羅馬式拼音方案確是一項技巧性很強的高難度工程，盡管有些方案比其他方案好，但任何方案都含有些無法憑直覺讀的拼寫。