Thanks for the great plugin. It fills our needs the best out of the several plugins I've tried so far and is far ahead of the dozens I read the description about and deemed unlikely to serve. Here's my feedback on how to improve it further:
Only after a while of searching I found out that the title of Daily Popular can be changed from the plugin options. It's good to have this option, and there's an even more logical place for it: have it as an option of the widget itself. This is how all WordPress default widgets and the best contributed ones do it.
Another problem I encountered was the formatting of the widget title. The cause was found out to be the <h3> tags around the title. No other widgets have this, so the theme we're using is not prepared for this either and the display comes wrong. I don't see any reason to do this, and it's easy to get rid of this when making the widget title option to be according to the de facto standard as suggested in the above paragraph.
By default the output for widget titles is:
<h2>Categories</h2> (displayed as blue and centered)
<h2>Tags</h2> (displayed as blue and centered)
<h2><h3>Daily Popular</h3></h2> (displayed as gray, larger than the above, and aligned to the left)
After removing the <h3> tags they are now displayed in the same way. There shouldn't be a reason to have users figure this out and fix it manually for themselves by having a non-standard way.
Other options should be moved to be widget options as well. There should be only one widget called Top 10, so a new user finds immediately what they just installed. Then that widget should have the option of the title, how many popular posts to display and from how many days. The help text would tell the user that when days = 0, it would show popular posts from all time (as the current separate Popular Posts widget does). The rest of the widget-specific options should be moved there as well.
This gives the site admins to make as many different widgets with Top 10 as they want and use it in the manner of their liking. Want to have a weekly top and monthly top without an all-time-top? You got it.
In short: Have only one widget, call it the same as the plugin, and move all widget-specific options to be set in the admin's widget panel.