1. They are both pretty much the same age..because they were made vampires around age eighteen.

2.  They both brood fabulously.

3.   Louis loved Claudia, a woman in a child's body. Angel loves( I stiill insist he does)Buffy, a young girl.......both girls are blonde....eerie isn't it?

4.  Both won't drink human blood, only animal blood.

5.  Neither are very humorous.

6.  Both killed humans and made them vamps for love.

7.  Both wanted to stay out in the sun and fry because they hate what they are..

8.  They both read a lot.

9.   Louis ran with Claudia and Lestat  and Angel ran with Spike and Drusilla. ....incidentally, Claudia and Drusilla both were obsessed with dolls.

10.  Angel and Louis both sired two vampires.

11.   Louis never lost his soul and Angel has basically regained his...a/k/a human souls trapped in vampire bodies

12.   Both were made vampires because  of thier devastatingly good looks.

13.   Claudia called Louis "My dark angel"......need I say more?

14.    Both are constantly seeking redemption for what they have done and what they are.

15.    Both hate thier makers for what they have done.

16.    Both wear really long black coats.....okay, maybe that's just a vamp thing

17.    There are almost identical scenes involving these two vamps with thier creators. In Interview with the Vampire, Lestat (Louis' maker) tells Louis he will only find peace if he kills humans. He says, "Pain is terrible for you. You feel it like no other creature because you are a vampire. You don't want it to go on. Do what it is in your nature to do. And you will feel as you felt when you had that child in your  arms. Evil is a point of view."
In the Buff y episode, "Angel", Darla (Angel's creator) tells him.."For a hundred years you've not had a moment's peace because you will not accept who you are. That's all you have to do. Accept it. Don't let her hunt you down. Don't whimper and mewl like a mangy human. Kill. Feed. Live!"