Something not many people know: when you need to compare 2 strings in C#.NET you can use the == operator overload:
if(firstString == secondString) { //... }
This is case sensitive. But when you need to ignore the case please don’t use this:
if(firstString.ToLower() == secondString.ToLower()) { //... }
or this:
if(firstString.ToLower().Equals(secondString.ToLower())) { //... }
A Framework provides you with utilities, please use them. They are usually better than your implementation!
Use this:
if (firstString.Equals(secondString, StringComparison.OrdinalIgnoreCase)) { //... }
StringComparison is an enum. So please look at the options 
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I prefer to use StringComparer:
StringComparer.OrdinalIgnoreCase.Equals (firstString, secondString);