I use Salifert and Seachem.. Seachem has awesome Customer Service however I feel that I can trust Salifert more... I am in the process of switching all my tests over to Salifert.. I should just do it all at once and buy the 209.00 master kit which includes all the tests... But I have spent enough money lately Better for me to do it slowly so the wife doesn't notice it as much..
I originaly got red sea kits when i got my tank. Iswitched to salifert after asking your same question here. I Love 'em. They are very easy to use and very easy to read a deffinite result. They're worth every penny.
Seachem is #1. Most of their test kits come with a liquid regent standard to check the accuracy of the test kit with. Also everyone is always sold out of alot of Salifert kits so they can be hard to get. Mainly because Salifert is horrible a supply distributors.