「誰がなんと言ったって[あだ名が]あった方がいい‼︎」
“no matter what anyone says, you should have one [a nickname]!!”
as shown in this panel from the 漫画 adaptation of 君たちはどう生きるか, the form Vたって is a casual form of Vても! if you need a refresher on that, here are the basic points:
Vても = even if you V; no matter how much you V (with wh-word*)
雨が降っても試合が続く。 = the match will go on even if it rains.
どんなに速く走っても、追いつけなかった。 = no matter how fast i ran, i couldn't catch up.
this form also works for い-adjectives...
忙しくても絶対来る。 = i'll definitely come even if i'm busy.
...and the copular で form works with な-adjectives and nouns:
いやでも、しなければならない。 = even if you don't like it, you have to do it.
先生でも間違いをすることはある。 = even teachers make mistakes.
and there you have it! keep your eyes peeled for the colloquial form—it crops up a lot! またね〜 🙋🏻♀️
*wh-words are words used to form non-yes/no questions, such as who (誰), where (どこ), and how (どう/どんなに).