In general, you get what you pay for.
I like the Salifert test kits for Ca, Alk and Mg.
One BIG plus of the Salifert test kits, IMO, is that they are titration based, which means you assess a sample based on a counting the number of drops until you see a colour *change*. The volume that gets added tells you what your levels are. The other method test kits usually employ is to have a colour intensity change and then you look up the colour on a chart and you decide which colour it most looks like. This is subject to more error in my opinion.
Elos also makes some good test kits that have a very solid reputation and are easy to use. I am not sure if they are titration based or colour-comparison based.
Another reason I like Salifert is that it measures Alk in meq/l. I like thinking of Alk in meq/l because a calcium reactor typically adds 10ppm of Ca to 0.1meq/l of Alk. The conversion of meq/l to dKH is 2.8, so the same sentence in dKH is "a calcium reactor adds 10ppm of Ca to 0.28 dKH". The math is easier when it's just multiples of 10
However many people talk about Alk in terms of dKH. So it's good just to remember the conversion.