no matter what; after all; in the end
Emphasizes that a statement holds true regardless of circumstances or objections. Often used to reinforce a reason or conclusion. Colloquial.
See also: なんてったって
No matter what you say, he's still a child, so he can't take on that kind of responsibility.
なんといったって、ここが一番落ち着く。
After all, this is the most relaxing place.
Contraction of 何と (what) + 言った (said) + って (quoting particle), literally 'even if (you) said what'. The exact historical derivation is uncertain, but it functions as a fixed emphatic expression.