which of the two computers games did you prefer?.

oth 与not连用,表示不完全否定,意思是事实上我不全都喜欢这两个,也就是喜欢一个,不喜欢另一个.
而either 用在否定句中,“(两者之中)任何一个 ”,意思是事实上这两个中的任何一个我都不喜欢.
例如
Either of the plans is equally dangerous.
这两个计划中,哪一个都同样有危险.
The news did not shock either of them.
这消息没有使他们任何一个人震惊.
I don't think either of them are at home.
我想他们中任何一个都不在家.
I have bought two books,you can have either.
我买了两本书,你要哪一本都可以.”

either 用在否定句中

问和答都有问题
为什么那问题不能直接以普通式来表达：
Whic of the two computer games do you prefer?
A不对，因为both不能出现在否定式里
应该：Actually, neither of them I like.

both 用于肯定句中I like both of them
而否定句中则应该用either(两个都不。).
I didn't like___B either of them____.