Hitman Absolution; normal edition or professional edition?

Normal.

Besides artwork the Professional version only adds 3 DLC that you can only use in Contracts mode.

Main story is pure base game.

Better wait for summer sale or 75% off if you want to get the special edition. And no, is not worth it if you don't like the artwork.
EDIT: 5 bucks on Amazon, 9 for professional

Most, if not all, of the extra content can be unlocked in-game, I think.
So no, it's not worth it.

Normal edition.

I would say no, since I think you only get to use the DLC weapons in contracts mode anyway. Also, 3 of the extra weapons can be purchased separately on Steam (may go as low as .25 cents during Sale).

I'm also trying to buy the Standard Edition from Amazon but unfortunately I only have a PP account

I'm at the checkout button now...

Ok I bought the normal one. I may want another one. LOL.

Professional edition comes with assassination insurance. Please be noted that it doesn't cover murders that look totaly like an accident and fiber wire strangulation cases.

http://www.buzzoonga.com/product/lp29941/hitman-absolution-professional-edition/