String vs char[]

The first string is stored in the 'intern pool' which is a special area of the managed heap. 

The second string is stored in the 'ordinary' heap.

When you use a string, it doesn't matter whether it's interned or not. It's just as easy for the CLR to read the string or any of its characters from the intern pool as it is from the ordinary heap and, since strings are immutable, any attempt to manipulate the string will result in  a new string being created in the ordinary heap.

The purpose of interning is to save memory as there will never be more than one copy of a given string in the intern pool. If two variables are assigned the same string literal, then they will both contain a reference to where that string is stored in the intern pool i.e. there will only be a single object, not two. 

Consequently, if a string can be represented by a literal (which is automatically interned) it's generally better to do so as well as making the code easier to read.