blue skies/vieather are uwp.
Nevermind 4castr isn't UWP which is a shame because if you do the trial on mobile you can customize it to hell. You can change which icons show up for different weather patterns like rain, snow, sun, etc.. You can then pin a tile and go through a wizard to select different tile options. It's pretty neat. Too bad it wasn't published to Desktop.
As far as Vieather and blue skies. Vieather is still a bit wonky, does have some nice live tile customizations but blue skies I would say is a bit cleaner so I would go for that. But honestly try them all nothing is stopping you. You may like one just because of some specific thing.