For ammonia I prefer LaMotte. Ammonia is toxic down to about 0.1 ppm, but I've heard (from Habib, so I assume it's true) that Salifert only reads down to 0.5 ppm. LaMotte reads down to 0.05 ppm.
The Salifert tests I have are for calcium and copper. I love the
calcium test. I hate the copper test. I use LaMotte for ammonia, NO2, NO3, pH and alk. All of those work well. I use Hach for phosphate and silicate. Both of those work well. I have the Hach Ca/hardness kit, but I find it completely useless -- Salifert is much better for Ca.
I have mixed feelings about the Salifert packaging. The good news is they don't charge for it. The bad news is it's really cheap. In the end I think I prefer the more expensive, better packaged kits, even if they don't work any better.