Certainly well done tats can be great but they're the exception not the rule and there's a certain line past which you end up looking like a back alley covered in grafitti.
Best tat ever in porn had to be Jandi Lin's.

Worst tat there's a lot of competition but this one on the right leg of Charlotte Sartre (also terrible name) may take the cake.

Bonnie Rotten's spiderweb tits are a close runner up.