这句话的意思是：

与其说我喜欢他的外表，不如说我喜欢他的性格。

这种“取舍关系”可以有多种表达：

I do not so much like his appearance as his personality.

I do not like his appearance so much as his personality.

It is not so much his appearance (that)I like as his personality.（强调结构）

I like his personality more than his appearance.