class Program
    {
        private static Random random = new Random((int)DateTime.Now.Ticks);
        static void Main(string[] args)
        {

            Console.WriteLine("Be patient, generating data...");

            List<string> list = new List<string>();
            List<string> toRemove = new List<string>();
            for (int x = 0; x < 1000000; x++)
            {
                string randString = RandomString(random.Next(100));
                list.Add(randString);
                if (random.Next(1000) == 0)
                    toRemove.Insert(0, randString);
            }

            List<string> l1 = new List<string>(list);
            List<string> l2 = new List<string>(list);
            List<string> l3 = new List<string>(list);
            List<string> l4 = new List<string>(list);
            List<string> l5 = new List<string>(list);

            Console.WriteLine("Be patient, testing...");

            Stopwatch sw1 = Stopwatch.StartNew();
            l1.RemoveAll(toRemove.Contains);
            sw1.Stop();

            Stopwatch sw2 = Stopwatch.StartNew();
            l2.RemoveAll(new HashSet<string>(toRemove).Contains);
            sw2.Stop();

            Stopwatch sw3 = Stopwatch.StartNew();
            l3 = l3.Except(toRemove).ToList();
            sw3.Stop();

            Stopwatch sw4 = Stopwatch.StartNew();
            l4 = l4.Except(new HashSet<string>(toRemove)).ToList();
            sw4.Stop();



            //Stopwatch sw5 = Stopwatch.StartNew();
            //l5 = l5.RemoveAll((x)=>x[0]==);
            //sw5.Stop();


            Console.WriteLine("L1.Len = {0}, Time taken: {1}ms", l1.Count, sw1.Elapsed.TotalMilliseconds);
            Console.WriteLine("L2.Len = {0}, Time taken: {1}ms", l1.Count, sw2.Elapsed.TotalMilliseconds);
            Console.WriteLine("L3.Len = {0}, Time taken: {1}ms", l1.Count, sw3.Elapsed.TotalMilliseconds);
            Console.WriteLine("L4.Len = {0}, Time taken: {1}ms", l1.Count, sw4.Elapsed.TotalMilliseconds);

            Console.ReadKey();
            //
            //authorsList.RemoveAll((x) => x.firstname == "Bob");

            //authorsList = authorsList.Except(authors).ToList();

        }
        private static string RandomString(int size)
        {
            StringBuilder builder = new StringBuilder();
            char ch;
            for (int i = 0; i < size; i++)
            {
                ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));
                builder.Append(ch);
            }

            return builder.ToString();
        }
    }

備註:這是網上找的例子大致方案就是這幾種，具體使用哪種看自己的實際需求

List集合刪除方法