I have both...Weather Widget Donate (WWD) and Beautiful Widgets (BW)
I switch between the two depending on the look I want.
The main widget layout is a little different for each but ss far as functionality they do the same thing:
They both tell weather and time
You can tap on different parts of the widget to launch apps of your choosing
They both have weather animation
They are both "skinable"
They both allow you to have transparent backgrounds
They both come with additional widgets for system toggles (bluetooth, wifi, silent etc)
WWD has an option to just show weather with no clock.
WWD allows you to skin the weather AND the clock separately
WWD allows you to view local weather cameras
BW has an option for a smaller Widget with clock and weather.
BW allows you to change the font color (I do not believe that WWD allows for this yet)
Personally:
I think that WWD flip clocks look better than BW.
I think that BW weather animation looks better than WWD.
I perfer BW for the non-flipclock look
BW has a better skinning tool...comes with preview pictures and is more user friendly
WWD had less skins but the ability to skin the weather is handy for themeing purposes
Both Developers are really good. They are both churning out TONS of updates.
I probably forgot some stuff