I enjoy rush mode very much, and I also do old school exploring. Drop rates seem to be the same. This last normal event i did 4 4hour rushes and got all cards except one. Did exploring and Arial dropped at lvl 40.
Last two wanderings have been to different experiences. Mammoth event was the worst ever for me. Got 1 drop in 600 kills. Eric was a lot better. 6 drops in 500-600 kills. Last nightmare city i choose not to use rush. I enjoyed doing it manually and got all 8 boss cards.