drops if you completely invert the bottle are as accurate as powders if not more(some may be left in the envelope), both are good
but definitely stay away from the strips, they are way too easy to corrupt, way too easy, this is a definite fact with the strips in general(not jsut aquarium usage)
IMO, i have had good luck with aquarium pharmaceuticals, but most people do not like them, and i can see now where they could be difficult to read properly, so i would not reccomend them highly, i have heard good things aout seachem and salifert, a friend of mine uses tetra and i like the readings, the colors are not even close on the different readings, so they are easier to distinguish for most people