which one is better?

其實不用揀了，因為第二句文法錯誤，那well-known piece並不能自己compose自己，故需用被動語氣，全句應為：
This well-known piece was composed in 1834.
若句子改成這樣，意思和第一句也有點不同。
This well-known piece was composed in 1834.（這出名的作品是在１８３４年寫成的）
而This was a well-known piece composed in 1834.（這是一出名的作品，於１８３４年寫成）
若更正後，兩句的意思都不同，就沒有哪個好了。
若在更改前，This was a well-known piece composed in 1834. 絕對比This well-known piece composed in 1834
希望幫到你！

前面個位~~
第2句文法的確有錯..
不過正確應該係
This well-known piece IS composed in 1834.
因為創作一直到現在還是存在的。

更正後其實兩句意思有所不同:
This was a well-known piece composed in 1834.
這個1834年創作的作品曾經很有名。(現在已經不存在/不出名)
This well-known piece IS composed in 1834.
這個著名的作品創作於1834年。(依然存在/仍出名)

不知作者要那個解釋?
把第一句改成
This IS a well-known piece composed in 1834.
就和第二句意思相同了。

This well-known piece composed in 1834.

This well-known piece composed in 1834.

個人認為第一個好d
指明係邊一個..