I will qualify my impression of 'best' as meaning: Best search engine for plugin database.

In this respect, I think that www.kvraudio.com and it's plugin database/search engine dominates over other sites listing plugins.

Very few developers do not register their plugins at www.kvraudio.com which means it's a fairly reliable place to see the latest plugins, to read user reviews of said plugins, to obtain download links, etc.

Many developers use www.kvraudio.com's forums as their 'official' support forum as well, it's so ubiquitous.

One service that they used to have, which they have not had for the past several years, was a user survey to define the 'best' pay and freeware plugins for various different categories. In a way, it was a 'wiki' for what the masses judged in these categories.