When comparing Ubuntu Mono vs Verdana, the Slant community recommends Ubuntu Mono for most people. In the question“What are the best programming fonts?” Ubuntu Mono is ranked 8th while Verdana is ranked 75th. The most important reason people chose Ubuntu Mono is:
There are dotted zeros in Ubuntu Mono so to distinguish from the letter "O", while the lowercase letter "l" is very different from the number "1".
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Pros

Pro Easily distinguishable characters
There are dotted zeros in Ubuntu Mono so to distinguish from the letter "O", while the lowercase letter "l" is very different from the number "1".
Pro Excellent readability
Line thickness, shape, and spacing help you to recognize characters and words correctly the first time through, without your eyes having to skip back and re-read.
Pro Pleasant aesthetics
The font has a rounded, smooth aesthetic that is particularly appealing.
Pro Many languages
1,200 glyphs, 200-250 languages (native languages of 3 billion people).
Pro Legible even at small sizes
The fonts retain legibility and under subpixel rendering at small sizes.
Pro Free with Windows
Pro Compact while light
Packs lots of information into your screen space while remaining clear and never looking crowded.
Pro Renders perfectly at all sizes
Again, particularly in Windows
Pro Looks absolutely gorgeous in Windows
Looks good elsewhere as well, but the world-class hinting here really comes out with the windows rasterizer (probably optimized for it).
Cons
Con Lowercase "m" is weird and stands out
The lowercase "m" in Ubuntu Mono really stands out because of its unusual shape, which disrupts the user's attention when reading.
Con Dotted zero characters less distinguishable
Dotted zero characters are much less distinguishable than those that are slashed.
Con Many characters seem imbalanced
Some of the characters don't feel like they match well which can be distracting.
Con No support for combined unicode characters
For example, x̄ is rendered as x ̄.
Con Not monospaced
-if that is an absolute must for you. But don't assume it is until you've tried without...