Which Harry Potter Translation is better
Short Answer

Both translations preserved most of the meanings in the original text. (Some by mistake and some deliberately dropped/altered for the smoothness of the overall context) 

For learning purposes, I would recommend the first one for its relative formality. If you are just reading for fun, the second one is more relaxing with its colloquial and conversational nature. 

Further Explanation

(If I made a incorrect comment on any of the translation, please point it out. Thanks!)


Translation Comparison


Below is a list of some obvious examples sentences, where the left is from the first translation:


  很早就醒来了 vs 一大早哈利就醒了


一大早 is unlike to be seen in academic/professional writing.


  那是个梦 vs 这是一个梦，，，


The use of ellipsis (I am not fond of the commas in place of … though) in a quote is informal yet vivid.


  我便会呆在家中 vs 我准在家里


The word 准 is used in conversations to mean 肯定、一定


  很响的敲击声 vs 啪啪的响声


Again, using 啪啪 to represent the actual sound is more vivid.


  



(Not-so-important) Error Picking 


The two translations have the following errors:


  学校学习魔法 


Well, from school for wizards to school to learn magic...魔法學校 is much better.


  折叠式的沙发上睡着了


Collapsed = 坍塌, Foldable = 折叠式. Although this detail is rather trivial to story progression and the plot.


  哈利感到特别高兴 ... 使他飘飘欲仙了


The translator dropped the scrambled to his feet and added these to sentences to emphasize his happiness... Perhaps creativity has been overly presented here.


  抓。” 是猫头鹰... (till the end)


I do not know what happened from here for the second translation. This part on is a bit chaotic, but otherwise it can be a good translation.