Lamotte makes the best Alk IMO, VERY high quality.
Elos Alk is very reliable, but I perfer the higher resolution of the Lamotte, than the ordinate values the Elos gives. I like to see the trend of the Alk if it is rising or falling to react sooner, still very high quality.
The Elos PO4 seems to be as good as it gets before making the leap to a Hanna.
I use Salifert for my Mg, Sr, Ca and they seem fine. Though most don't test Sr, (I decided to try just to see what would happen and the jury is still out), regardless don't let the Sr sticker price scare you off, its a Ca test as well!!!! Cool huh?
The "best" test is the person running the test. Do it accuratly with rinsed, clean equipment each time. Take your time and repeat with multiple kits if you can. I used to do it sitting in front of the tank and found I rushed them and was sloppy. Now I soak 2 plastic containers, soak the vials in one to rinse them clean and use the other as my test source. I take them back to the desk and take my time doing them.......sometimes even while typing responses like this........gotta go, my Sr is finished sitting.