Are you asking about API or just about weather data source for forecast? I was comparing many data sources over many weeks and my results in Prague were Aeris

Are you asking about API or just about weather data source for forecast? I was comparing many data sources over many weeks and my results in Prague were Aeris weather most accurate (least false positives/negatives for rain), then gap and Foreca and MET Norway same and then big gap and you have very bad sources like Dark Sky, AccuWeather, Weatherbit and Open weather which are unusable. As for the mobile apps on Android I use Weawow (has all 3 most accurate sources) and Today Weather (no Aeris, but had Foreca and MET Norway). I'd recommend these two apps and comparing sources for few weeks to find out which one is the most accurate for your location, because accuracy varies across different locations, so there won't be single correct universal answer what you should use.