Another plug for salifert. With the exception of the phosphate test, they are very easy to read. You don't have to try to compare a fluid color to a printed color chart. You basically do a titration with graduated syringe and then look up the test result on a chart based on the amount of titrant used. There is a good, hard color change so guesswork is kept to a minimum. They also seem to be quite consistant.
The phosphate test is the only one I've run across where you have to try to determine the color of the liquid -- works a little better if you follow the instructions for running a higher sensitivity test.