The most frequently 'iodef' records are shown here.
Pretty pleased to see Yahoo's records dominate, since setting the right CAA policy and adding default CAA records for all of Yahoo's (many) parked domains was something I pushed for at my time there. Yay! \o/
But let's see what CAs everybody is authorizing via their 'issue' and 'issuewild' records.
In total, I found almost 2,200 distinct 'issue' records (for domains in all TLDs, 456 distinct for the Top 1M domains) and 878 'issuewild' records (all TLDs, 227 Top 1M).
Here are the top 20 CAs: