Hard to argue with under $5 .iPhone 5 covers from monoprice.com. Very inexpensive.
I have tried many styles, and TPU is my second favorite kind!
Thermoplastic Poly Urethane (if I can spell)
It's a tough translucent shock-absorbing material (not soft nor springy)
Some cases like those at Monoprice have a hard outer shell.
TPU alone is fine (too) and provides a non-slip surface.
I won't recommend the silicone nor spongy rubber cases.
These are too soft and too grippy coming out of your pocket.
And of course, your mileage may vary.
iphone 4