Iterates over amplicon tuples and returns the one with highest quality
        and amplicon length.

def choose_best_amplicon(self, amplicon_tuples):
        """Iterates over amplicon tuples and returns the one with highest quality
        and amplicon length.
        """
        quality = 0
        amplicon_length = 0
        best_amplicon = None

        for amplicon in amplicon_tuples:
            if int(amplicon[4]) >= quality and int(amplicon[5]) >= amplicon_length:
                quality = int(amplicon[4])
                amplicon_length = int(amplicon[5])
                best_amplicon = amplicon

        return best_amplicon