VowelIndices in my way and as lambda/RegularExpression

VowelIndices in C#.cs

        private static int[] VowelIndices(string word)
        {
            List<int> myVowelList = new List<int>();

            for (int i = 0; i < word.Length; i++)
            {
                switch (word.ToLower()[i])
                {
                    case 'a':
                        myVowelList.Add(i + 1);
                        break;
                    case 'e':
                        myVowelList.Add(i + 1);
                        break;
                    case 'i':
                        myVowelList.Add(i + 1);
                        break;
                    case 'o':
                        myVowelList.Add(i + 1);
                        break;
                    case 'u':
                        myVowelList.Add(i + 1);
                        break;
                    case 'y':
                        myVowelList.Add(i + 1);
                        break;

                    default:
                        break;
                }
            }
            int[] myVowelArray = myVowelList.ToArray();
            return myVowelArray;
        }

VowelIndices2.cs

        public static int[] VowelIndices2(string word) =>
                new Regex("[aeiouy]", RegexOptions.IgnoreCase).Matches(word).Cast<Match>().Select(m => m.Index + 1).ToArray();