I've pretty much given up on cases, and I'm thinking I may be giving up those screen protectors too.
I had a screen protector on my 3GS for about two years.
EDIT: Oops, I completely forgot to write the rest of this part...
I stopped using the screen protector after that. It just always got gunky, and my screens have never gotten scratched. Most of the scratches that I incur tend to happen from setting the phone down. My 4S, which has always been in a case, looks fantastic and it only ever had different cases.
Here's the case that I used last with it:
http://www.monoprice.com/products/product.asp?p_id=7109
Before that, I used the clear variation of it, but I hated the weird crystal pattern on the back. It just looked... well, too "Bedazzled" for my tastes. I also used a
Tyrael case from PDP, but it doesn't cover as much of the phone, and the slight nick on the top is probably from the case not protecting the phone from me trying to plug the 3.5mm cable. It was also a bit thicker, which I didn't care for.
how does lifeproof compare to otterbox? lifeproof is waterproof isnt it but does it protect your phone better than otterbox?
I don't own one, but my friend had her phone in an Otter Box and now its in a Lifeproof case. She pretty much swears by the thing and is definitely willing to
show you that it is sturdy. She told me about how a friend asked her about the case and she just threw it against the wall. Saying that was enough to make my face look like this:

! Her opinion is that the Otter Box is simply too big. She also has some similar complaints as other users that the headphone jack adapter is rather easy to misplace and you
have to have it.
I recall reading a review for the case where the guy originally didn't care much for the case, but he later revised the review stating that the phone fell out of his pocket... while riding a motorcycle and was apparently run over by a car. The phone was slightly damaged, but considerably less than you would expect for all of that.
If you're interested in one, I'd say keep your eyes pealed for a good deal. I recall seeing a 20% off coupon for phone cases at Best Buy
Mobile (this is different than the normal Best Buy stores), which would include the Lifeproof case (-$16).