I only have nylon martingales. It's all I ever use, puppy and adult dogs alike. I don't use them to "correct" a dog. I have them because I've come across too many dogs that like to back out of a collar. Plus I've had sighthounds for 14 years, and thats all we ever use on them.
Just get a nylon martingale, and make sure you fit it properly.
~ Diane in Okla
Carly ~ AKC Ch, GCh pointed, HIC
Sage ~ AKC Ch pointed (chasing that last major), HIC
Russell ~ future show dog
Zelda ~ puppymill rescue Italian Greyhound