What is better for an iPhone 4?

What I better for an iPhone 4? A spray on screen protector or plastic screen protectors?

Plastic screen Protectors are best They last long for like 6 to 12 months. Sprays are not good they last long till one month Screen Protector Are also good:-)

A plastic screen protector is better for any device. A spray-on screen protector has to be re-applied every 3 months.

You know what, iPhones come with one if the best glasses seen anywhere in mobiles.
Gorilla glass is its name and it is highly tensile and extremely resistant to scratches.
Also a useful thing is, it comes with an oleo phobic coating on the front and rear which automatically wipes away all the finger prints on the iPhone. So I would suggest that you should use it without any screen protector as Apple has thought about all the possibilities and given great solutions.

Also screen protectors makes you leave all of your fingerprints in the screen making it dirty to use.

Plastic. Mines been on since I got it. Nearly 2 years now