StringComparison

Here is a great article on when to use the StringComparison.

http://msdn.microsoft.com/en-us/library/ms973919.aspx

DO: Use StringComparison.Ordinal or OrdinalIgnoreCase for comparisons as your safe default for culture-agnostic string matching.

DO: Use StringComparison.Ordinal and OrdinalIgnoreCase comparisons for increased speed.

DO: Use StringComparison.CurrentCulture-based string operations when displaying the output to the user.

DO: Switch current use of string operations based on the invariant culture to use the non-linguistic StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase when the comparison is linguistically irrelevant (symbolic, for example).

DO: Use ToUpperInvariant rather than ToLowerInvariant when normalizing strings for comparison.

DON'T: Use overloads for string operations that don't explicitly or implicitly specify the string comparison mechanism.

DON'T: Use StringComparison.InvariantCulture-based string operations in most cases; one of the few exceptions would be persisting linguistically meaningful but culturally-agnostic data.