I use a brand called Elos, which seems to be good. I think its made in italy. I also have some salifert test kits, which are also supposed to be accurate.
Can't say I'm using anything right now... but API is fine for testing. They kits are rather accurate. I would recommend something like their reef master kit and then do a Elos Mg test as well. I don't buy ammonia & nitrite test kits. Waste of money.