When comparing Kaleidoscope vs BBEdit, the Slant community recommends BBEdit for most people. In the question“What are the best folder/file compare/diff tools for either OSX, Linux or Windows?” BBEdit is ranked 7th while Kaleidoscope is ranked 12th. The most important reason people chose BBEdit is:
BBEdit is commercial software, the paid counterpart to their free application Textwrangler. Though BBEdit comes off as pricey, this allows for stable and consistent updates from the developers. BBEdit has been around since 1992.
Specs
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Pros

Pro Simple UI
Kaleidoscope has a beautiful and simple UI. It displays the two files that are being compared side to side, highlighting all the differences in a way that's easy to understand.
Pro Diff within a line
When working in code, line-by-line diff can still be hard to spot small changes within the line. Kaleidoscope will highlight what has changed.
Pro Supports comparing folders

Pro Image difference viewer
Kaleidoscope supports image diff viewer in addition to git diff. It's able to find even the slightest changes between two versions of the same image.
Pro Stable development, been around for decades
BBEdit is commercial software, the paid counterpart to their free application Textwrangler. Though BBEdit comes off as pricey, this allows for stable and consistent updates from the developers. BBEdit has been around since 1992.
Pro Can open very large files
Pro Just about every feature is already built in
No searching for plug-ins that may or may not work.
Pro Great customer support
The developer is very responsive to bug reports and feature suggestions.
Pro Native application
Follows platform standards.
Pro Built-in FTP/SFTP browser
BBEdit can open files directly from, and save them to, any available FTP server. It can also open and save files directly via SFTP (SSH File Transfer Protocol).
Pro Great JAMStack environment
You can build the static site of your dreams without needing any external assistants. Although it does not process LESS, SASS, or SCSS files, BBEdit's includes are very powerful.
Cons

Con Mac OS only
Kaleidoscope is a Mac OS X only app.
Con Paid software
Kaleidoscope is not free, costing $69.99.
Con Featureless
Con Expensive
It's US$49.99 a single user license.
