I use API, just cause it's the only brand of master test kit that is sold in the stores here. And I'm not big on ordering things online unless they're ridiculously expensive in store.
Don't think it matters much, they're both accurate and reliable, imo, just pick the cheapest one. After your tank is established, you'll rarely need to pull the test kit out anyway. I've still got craploads of contents left in my API kit, but I don't really use it anymore cause there isn't much of a need to when your filter is cycled and you keep up with your water changes.
And if you notice something wrong with the fish in the future, you'll know by then that a water change the first thing you want to do, and all the things test kits measure are combated by water changes. No real use in testing the water to see if you should do a water change when you really should anyway if you notice things wrong that might be due to ammonia, nitrate, or nitrite.