prefer 搭配的介词是 to, prefer A to B. 只有A、B 均为 to do 不定式时，采用than取代to, 避免二个 to 重叠。

prefer 名词A to 名词B

prefer doing A to doing B

prefer to do A than to do B

本句用 rather than为错误，应改为 to。

I prefer travelling by train rather than travelling by plane, for trains are cheaper, safer and more comfortable.

更正为：I prefer travelling by train to travelling by plane, for trains are cheaper, safer and more comfortable.

请问这句话到底哪一个划线部分有错误？  是rather than吗？（但是rather than后面可以跟Ving 吧？）

prefer主要有以下几种搭配

(1)主语+prefer doing sth(A)to doing sth(B)

I prefer skiing to skating.

我喜欢滑雪胜于滑冰。

I prefer doing this to doing that.  

我宁作这事,不愿作那事.

I prefer doing practical exercise to working at grammar.  

相比学习语法,我更倾向于做实际的练习.

(2)主语+prefer A to B

I prefer country life to town life.

我更喜欢乡村生活而不喜欢城市生活。

I prefer red to blue.

我更喜欢红色而不喜欢蓝色。

Most Chinese preferred tea to coffee.

茶和咖啡相比大多数中国人更喜欢喝茶。

(3)主语+prefer to do sth rather than do sth

They preferred to stay at home rather than go to the movies.

他们宁可呆在家里,也不愿去看电影。

They preferred to die rather than surrender to the enemy.

他们宁死也不愿向敌人投降。