string-Compare

        // Provides a culture-correct string comparison. strA is compared to strB
        // to determine whether it is lexicographically less, equal, or greater, and then a
        // negative integer, 0, or a positive integer is returned; respectively.
        // The case-sensitive option is set by ignoreCase
        //
        [Pure]
        public static int Compare(String strA, String strB, bool ignoreCase)
        {
            if (ignoreCase) {
                return CultureInfo.CurrentCulture.CompareInfo.Compare(strA, strB, CompareOptions.IgnoreCase);
            }
            return CultureInfo.CurrentCulture.CompareInfo.Compare(strA, strB, CompareOptions.None);
        }

Console.WriteLine(string.Compare("EABA", "EaBA", true));// 0

ignoreCase=true是不区分大小写。