<?php
$words=['MVW','MWAH','MWAH','MYW','MW','MY9AH','MYQAH','MYQAH','MY9AH','MYQAH',
'MYQAH','MWAH','MYQAH','MYSWI','MYQAH','MYQAH','MW','MW','MW','MW'];
$chars=array_map('str_split',$words);
usort($chars,function($a,$b){return sizeof($b)-sizeof($a);});
$result='';
foreach($chars[0] as $col=>$not_used){
$occurrences=array_count_values(array_column($chars,$col)); // no NULL values
arsort($occurrences);
$result.=key($occurrences);
}
echo $result;
preferences:
49.25 ms | 402 KiB | 5 Q