Ask HN: What is the best rating system?

Bonjournal is a journaling app that helps you document and share your travels.

https://bonjourn.al

We are thinking of adding a rating system so that users can rate the places they visit. Think journaling meets Yelp / Foursquare.

Obviously no rating system is going to be perfect. Yelp uses the five star system. Foursquare uses a 10 point scale. We are leaning toward letter grades.

Why I like letter grades:

1) Precision: A, A-, A-/B+, B+ 2) Less ambiguous: I have a strong understanding of what a B vs a B+ means...not so much with 6.5 vs 7 or 3.5 stars vs 4. Perhaps that is just me. 3) Widely adopted: http://en.wikipedia.org/wiki/Grading_systems_by_country

However, we're not 100% sold, and wanted to ask the HN community.

* What rating system do you prefer and why? *

Some references:

http://techcrunch.com/2009/09/22/youtube-comes-to-a-5-star-realization-its-… http://www.quora.com/Is-there-a-better-alternative-to-the-5-star-rating-sys… https://www.quora.com/How-reliable-is-the-100-point-scoring-system-for-choo…