新建一个Person类

public class Person
    {
        public Person(string name,int id)
        {
            Name = name;
            Id = id;
        }
        public string Name { get; set; }
        public int Id { get; set; }

    }

初始化List中有一百万条数据，然后分别通过每种方法判断xiaoming是否在List中，代码如下

static void Main(string[] args)
        {
            List<Person> persons = new List<Person>();
            //初始化persons数据
            for (int i = 0; i < 1000000; i++)
            {
                Person person = new Person("My" +     i,i);
                persons.Add(person);
            }
            Person xiaoming=new Person("My999999",     999999);

            //下面通过三种方法判断persons中是否包含xiaoming
            Stopwatch watch = new Stopwatch();
            watch.Start();
            bool a = persons.Contains(xiaoming);
            watch.Stop();

            Stopwatch watch1 = new Stopwatch();
            watch1.Start();
            bool b = persons.Exists(x=>x.Id==xiaoming.Id);
            watch1.Stop();

            Stopwatch watch2 = new Stopwatch();
            watch2.Start();
            bool c = persons.Where    (x=>x.Id==xiaoming.Id).Any();
            watch2.Stop();

            Stopwatch watch3 = new Stopwatch();
            watch3.Start();
            bool d = persons.Any(x => x.Id ==     xiaoming.Id);
            watch3.Stop();

            Console.WriteLine("Contains耗时：" +     watch.Elapsed.TotalMilliseconds);
            Console.WriteLine("Exists耗时：" +     watch1.Elapsed.TotalMilliseconds);
            Console.WriteLine("Where耗时：" + watch2.Elapsed.TotalMilliseconds);
            Console.WriteLine("Any耗时：" + watch3.Elapsed.TotalMilliseconds);
            Console.ReadLine();
        }

执行结果如下图所示在这里插入图片描述

通过上图可以看出性能排序为 Contains > Exists > Where > Any

注意： 上面Contains的结果为False，因为即便xiaoming和list中的对象相等，它们储存的地址也不同。感谢@饺子快跑的提醒