The one in my profile picture is the absolute favourite. :)
But, I like basically any coin from Danzig. No matter the age or condition. I also like the 10 Stotinki coin from Bulgaria from 1881, due to the flowers on the obverse:
This superb paisa of Mysore is my favourite, I purchased it way back in 1961 aged 15 and it set me on the way to collecting Indian coins up to today. It's reverse has an unrecorded variation in the script