If in the US most people go with eithor API as they can be found in just about any LFS here in the States, and the cost is reasonable. Hagen Nutrafin, is also popular here in the US, but usually needs to be purchased on-line, price is roughly the same as the API (I believe the Hagen Nutrafin kits are easily found in Canadian LFS). Saliferts are also good, but again can be hard to find unless you order on line they can also be very pricy in the US, but from my understanding Saliferts are much more readily available and cheaper in the UK. Eithor of those 3 brands are good, as for which one is the best it really comes down to user prefenence, personally I use the API kits and have never had problems.