It depends on what look you are going for.
The '03-'04 cobra bumpers are nice looking but you have to be willing to jump on the bandwaggon as it seems that is the bumper that a lot of people are upgrading to.
Cobra R just looks mean.
Saleen looks kinda artsy with all of its creases.
The kaminari is pretty cool, but you have to be willing to do the hood too.
I just purchased a '99, '01 cobra font bumber a few days ago. They are by far my favorite. I like the look best because it is subtle but tough.
So yeah, to quote whyask "WHAT DO YOU LIKE...???" and what is your overall goal for the car?