as to the best way 和 as the best way 两种情况都可能存在.as to the best way 以as to 开头,意思是“至于最好的方式...”；as the best way 以as开头,意思是“作为最好的方式”.
As to the best way to improve oral English,I recommend you to practise and practise.
As the best way to improve oral English,crazy English is very popular.