I have both widgets....I LIKE both widgets. I find I switch between the two depending on my mood. I CONSTANLY mess with my display/wallpaper/clock and weather. I like to mix it up, and I am always trying out new looks
Here is my comparison.
Similarities: Both cost about the same (1.50 US if I recall). On the home screen both display time, location, date, a current weather graphic, a current weather description and a "H" and a "L" temp for the day. When Tapped they launch a full screen view of the current weather graphic with fancy animations such as clouds or rain. (weather widget donate requires an additional free down load for the animations). At the bottom of the full screen view is a three day weather forecast (weather graphic with a high and low temp) . They both have settings where you can: have the weather shown for a specified location or your actual location (uses GPS i guess), adjust the update frequency or force update the app, set the time to the 24 hour format, set the temperature to Celsius, adjust the sun/moon timing . They both have an option to down load skins to change the look and feel of the widget. Both have digital clock and flip clock style skins. The skins seem to be made by enthusiast and the population of skins for each app seems to be increasing. Both look damn good. Both have different size widgets
Differentiators:
Weather Widget donate: Allows for weather skins as well as clock skins allowing for more customization. Weather widget donate has 4 sizes of widgets: Clock and Weather (largest), Weather Large, Weather Small, Weather Tiny (Only the clock widget shows the time). Weather widget donate allows you to set up an app shortcut when you tap the three day forecast on the full screen view...pretty handy to tie in a weather app to that to get a deeper view. You also have an setting that allow you to launch the stock alarm app when tapping the clock widget if you don't care for the full-screen-pretty-animation-three-day-forecast-view. Layout: Weather graphic in the middle of the clock
Beautiful Widgets: In addition to the Home Widget (the clock and weather) you get toggle widgets for GPS, Bluetooth, Plane, Silent, Vibrate and Wifi. You also get a 1X4 Smaller Home Widget that displays the time as well as the weather (same info as the larger home widget). The tool that allows you to change the skins provides a preview (skins preview absent in weather widget donate as of 1/27/10), which is very handy. In the stock layout you can change the font of the clock. You have three fonts to choose from Android, Bloodwax an Tahoma. Layout: Weather graphic under the the clock to the left side of the screen.