Performance of LINQ Any vs FirstOrDefault != null

Question

There are multiple places in an Open Source Project (OSP) code I contribute, where it has to be determined if an element in a collection satisfies a certain condition.

Answer 1

The problem with this question is that it is not asked within context. I am providing an answer because I see this a lot in code reviews and it bothers me. LINQ should not be an excuse to stop thinking.

var people = new [] { "Steve", "Joe" };

if (people.Any(s => s == "Joe"))
{
    var joe = people.First(s => s == "Joe");
    // do something with joe
}

// if people is 1,000,000 people and joe is near the end do we want BigO to approach 2N here at worst case ?

var joe1N = people.FirstOrDefault(s => s == "Joe");
if (joe1N != null)
{
    // do something with joe
}

// or do we want to ensure worst case is N by simply using a variable ?