You could be in for some trouble because they both come in packages saying underjams made by pampers, and i believe its close to the same for goodnights.
If you mean wearing: I know all about Goodnites. I've worn them for... about 12 years now. Probably a little longer.
Anyway... they are fairly slim. They don't bulk too much so they won't show too well if you're wearing something like jeans. They can be noisy sometimes but not as noisy as most other diapers. Just watch your waistline though. Wear something like boxers over your Goodnite (it WILL show).
I prefer Underjams to Goodnites. For one thing, Underjams don't make hardly any noise. There is some, but it's actually quieter than the sound a pair of jeans make normally, so it's not a problem. Goodnites are very noisy, though. Also, Underjams are stretchier than Goodnites, although the stretchy material isn't as robust as the material on a Goodnite. The only downside if you're going for stealth is that Underjams are about three times thicker than Goodnites.