When choosing whether to go with nylon or steel garage door rollers you will need to consider a couple of things and decide what is more important to you. Both are excellent choices, but each kind has its own benefits.
If you want as little noise and vibration as possible when your garage door opens and closes, then nylon garage door rollers are your best option. Because they are made with nylon, they aren’t as noisy as steel rollers and they don't cause as much vibration. If you live in a quiet neighborhood and work shift work or tend to be out late, then nylon rollers will cut down on the noise your garage door makes.
Steel is a much harder material than nylon, so steel garage door rollers will last a lot longer than their nylon counterparts. If the thought of changing your garage door rollers every few years gives you a headache, then stick with the steel rollers, since you can get around 20 years out of them.