Title case or sentence case is not a decision worth a long meeting, but it is worth making once and enforcing, because the cost of not deciding is paid on every page forever.
What each signals
Title case reads as traditional and editorial — news, established publications, formal reporting. Sentence case reads as modern and conversational, and it is what most software products and newer publications use.
The case for sentence case in search results
A page title in sentence case tends to look less promotional in a results page, sitting closer to how the surrounding interface presents text. Title case can read as more authoritative for editorial content. Neither affects ranking; both affect whether the result looks like something a person wrote.
Enforcement is the actual problem
Pick one, write it in the style guide, and normalise the existing archive in a single pass. A convention nobody applies retroactively is not a convention, just a preference nobody follows.
Try it: Convert Text to Title Case on SeoWolf's Notepad.