If you're using LINQ on a list, it will not use Expressions, but a plain Func. So nothing will get parsed either way. The difference, as @sbelskie already ment

If you're using LINQ on a list, it will not use Expressions, but a plain Func. So nothing will get parsed either way. The difference, as @sbelskie already mentioned, is that Where has an optimization for List, while First only uses the naive enumerator.