C# .First() vs [0]

Question

Interested, does approaches has any differences.
So, I created two snippets.

Snippet A 
List a = new List();
a.Add(4);
a.Add(6);
int         


        

Answer 1

The Enumerable.First method is defined as

public static TSource First(this IEnumerable source) 
{
    if (source == null) throw Error.ArgumentNull("source");
    IList list = source as IList;
    if (list != null) {
        if (list.Count > 0) return list[0];
    }
    else {
        using (IEnumerator e = source.GetEnumerator()) {
            if (e.MoveNext()) return e.Current;
        }
    }
    throw Error.NoElements();
}

So for a List it ends up using the indexer after a null check and a cast. Seems not much, but when I tested the performance, First was 10x slower than the indexer (for loop, 10 000 000 iterations, release build: First - 100 ms, indexer - 10 ms).