It's hard to even look closer at anything comparable once pinboard has become the main destination for anything bookmark related.

I have been using it for years and since it's API is based on the original Delicious one there is most surely not a single tool out there that does not speak to Pinboard.

While there might be quite a few alternative solutions our there that are feature wise on par with (or better than) Pinboard - the latter one has a proven track record and a positive future outlook.