What makes have proven to be the best?
Dangerous question, as it really depends on your budget, and how obsessed you'll become with chasing correct parameter "numbers" and accuracy and precision.
The sad reality is that a lot of hoby grade kits are no good for anything more than an indication..... Which is often, but not always good enough.
Hereby recommendations of brands which have worked for me:
Ammonia: Seachem ammo alert. A little sticker that does a great job of warning you of ammonia levels.
Nitrite: Salifert
Nitrate (sorry, forgot this vital one in post above) I would go for the New Red Sea Range.
pH, nothing less than a pH pen. The milwaukee brand is awesome for entry level as well as their Martini range of Laboratory toys.
Salinity, nothing less than an ATC refractometer. Try Milwaukee or Deltec. Stay away from the cheap Chines junk.
Calcium: Seachem, or, if you are willing to import, get your hand on some La Motte. Bigger budget, get one of those checkers from
@Andre@ReefAquatics
Alkalinity: Salifert, or again, if you willing to import your own, get a La Motte. Bigger budget, get one of those checkers from
@Andre@ReefAquatics
Magnesium: Salifert is good enough, or if you have a huge budget, get the seachem, which is great as it measures borate alkalinity too.
For PO4, I would not waste any money on hobby grade kits, unless you are willing to pay for a Hach / Deltec kit, which is very close in price IIRC to the Hanna mini photometer checkers sold by Reef Aquatics.
Strontium, Seachem
Iodine, Seachem
Think I have covered most of them now...