All the others use their data anyway, so you might as well just get it from the source.
I particularly like their uncertainty estimates - if you understand how to use them, they're brilliant. They are totally upfront about how uncertain they are - so you can make your own call about whether to rely on the prediction or not.
Generally speaking, it seems to me that they are all much the same. As Mungo says, it's all from data from the Met Office so it comes down which way you like it presented.
Again generally speaking, they are all excellent at telling you what the weather was yesterday. They're pretty good at telling you what the weather is doing today. They are fairly good at telling you what it'll do tomorrow. The day after is usually worth looking at. After that, things become more woolly the further into the future you go.
My system for weather forecasts is to scroll through the regional news channels and watch the dishiest weather girl, I can highly recommend Kealey on BBC Yorkshire!! The reasoning behind this is I'm convinced they can't tell you if it's going to be light or dark at a given time never mind if it's going to be dry or bloody wet, I might as well watch someone pretty giveing me duff Info!!!
About the best! This is almost gospel for those that fly model gliders on the coast or on the moors. I do use the BBC weather app on the ipad for an idea of the weather when I am going shooting, but the linked weather site has far more detailed information and is much more than a shooter will need whilst conducting a leisure pursuit.