Shell script help

How can I change my code to be able to compare the size of two files.

if [ -f $1 ] && [ -f $2 ] && [ ! $1 -ef $2 ]; then
    size1=$(du $1)
    size2=$(du $2)
    if [ $1 -gt $2 ]; then
     echo "$1 is bigger"
    else
      echo "$1 is smaller"
    fi
fi

look at these sepples. They are ugly. Behold the true power of shell.

#!/bin/bash

function fz()
{
    echo $(wc -c <"$1")
}

a=$(fz a.sh)
b=$(fz b.sh)

echo $(($a < $b))
echo $(($a == $b))
echo $(($a > $b))