Try Carrot on iOS. It is really good. It is famous for its mini game and snarky robot comments that predict the weather. But the core weather is great and has the best interface.
Carrot, by default, uses the Dark Sky API. It's one of the few apps that lets you choose an alternate data source. Wunderground used to be the best choice, but that API vanished last year. With Dark Sky gone, none of the remaining options are particularly good, if you live in the USA.