Most efficient way to concatenate strings?

Question

What\'s the most efficient way to concatenate strings?

Answer 1

If you're operating in a loop, StringBuilder is probably the way to go; it saves you the overhead of creating new strings regularly. In code that'll only run once, though, String.Concat is probably fine.

However, Rico Mariani (.NET optimization guru) made up a quiz in which he stated at the end that, in most cases, he recommends String.Format.