I asked around while trying to learn how to use LINQ. LINQ is essentially SQL for .NET—it allows you to query objects directly in memory. For example:

List<int> test = new List<int> { 1, 3, 5 };
List<int> testnew = (from a in test where a == 5 select a).ToList();

Someone claimed LINQ was faster than using foreach for selecting items. So, I tested it.

The Benchmark

static List<int> testlist = new List<int>();

static void Main(string[] args)
{
    DateTime b, a;
    List<double> regularTimes = new List<double>();
    List<double> LINQTimes = new List<double>();

    for (int x = 0; x < 1000000; x++)
        testlist.Add(x * 5);

    // Foreach loop test
    for (int x = 0; x < 1000; x++)
    {
        b = DateTime.Now;
        TestRegular();
        a = DateTime.Now;
        regularTimes.Add((a - b).TotalMilliseconds);
    }
    Console.WriteLine("Regular Avg.: {0}", regularTimes.Average());

    // LINQ test
    for (int x = 0; x < 1000; x++)
    {
        b = DateTime.Now;
        TestLINQ();
        a = DateTime.Now;
        LINQTimes.Add((a - b).TotalMilliseconds);
    }
    Console.WriteLine("LINQ    Avg.: {0}", LINQTimes.Average());

    Console.ReadLine();
}

private static void TestRegular()
{
    List<int> newlist = new List<int>();
    foreach (int item in testlist)
        if (item % 2000 == 0) newlist.Add(item);
}

private static void TestLINQ()
{
    var newlist = (from a in testlist where a % 2000 == 0 select a).ToList();
}

This runs each selection method 1000 times on a list of 1,000,000 items.

Results

Regular  Avg.: 81.64 ms
LINQ     Avg.: 84.31 ms

Conclusion

The difference is negligible and could be attributed to background system noise. Based on this test, LINQ and regular iteration perform similarly.

Use whichever fits your coding style and needs.