You can ask this and probably get a different answer for each comment! It really depends on what you want from it and what data sources work best where you live. I'll mention a few:
Forecaster is super simple, displaying the forecast for each day as a bar. Yellow represents clear weather, grey represents cloud, and so on. I quite like it, although you can only see weather, temperature and wind, and it uses Apple Weather with no option to use something else.
Clyma is by far my favourite. It looks the best and offers the most data (like wind gust and feels like temperature) and displays it in a graph. Although it's very unreliable, and sometimes stops refreshing entirely. I have to clear the app's data, then enable the location permission before I launch it again to get it working. So I can't rely on it that much.
Overdrop is a little bit like Clyma but it hasn't made it onto my new phone.
Today should get a mention. I don't use it much but it's got by far the biggest array of sources to choose from, and you get data on air quality that you don't see much elsewhere.
Meteogram is great if you really like customising and getting into the data itself. You can completely change how the graph looks and what data is included. I bought it on sale a while back and still have access to the old "Credits" system, so I can't speak for how the new subscription model works but there's still a free tier.
Forecastie and OpenWeather are nice ways to access OpenWeatherMap data if that's what you prefer.
The Met Office app is a nice way to get notified of warnings if you live in the UK.
And RainViewer is a very nice radar app, but the imagery doesn't seem to update very often here (even with Premium, which is meant to give you a 5-minute resolution. Other apps have this imagery, so I don't quite know why they don't because they definitely used to)
It has a really nice minimalistic widget with whtatever weather info you want for a location and it also integrates a clock with it, so its like 2 widgets in 1
IIRC Weawow has Apple weather as a provider, which is basically a rebranded Dark Sky (check out Apple's weatherkit for more info about this rebrand thing)
Ok, I thought they removed when Apple bought it. I remember seeing it in a change log, maybe I'm wrong or they brought it back under Apple branding. In my older version the provider shows up as Dark Sky (Apple).
I really like Weather Today since it has Apple's weatherkit data, which is basically Dark Sky. It also has a really nice radar view and a per minute rain forecast. There is also Shadow Weather which has this support, but I find the UI to be less appealing.
I've found Windfinder to be really good for me. It's not as flashy as the others out there, but it's been really accurate and detailed which I value more than other features.