Colonials. Seems like a natural progression for any numismatic that has studied early US coinage to move into them. I'm surprised that so few collectors on this forum collect them. They provide a glimpse into the deeply rich history of the founding of our country. I love everything about them. From the primitive designs to the vast availability of different issues. I actually approach them backwards. I find a coin that intrigues me, I check previously sold listings to get an idea of pricing and I bid on it. If I win it, I spend the next few weeks learning about the coin and its history. I really enjoy this approach.
Morgan's were my first passion, so that series is probably my favorite to collect and study. After that I would say an interest in the beauty of the capped bust design, particularly the halfs, which currently have my attention.
I am a fan of the Barber series. It exudes a certain elegance to it that I think is unmatched. The reverse eagle signifies the United States as a logo better than anything I have seen. I absolutely dislike blast white, only stay with original toned mint state.
All of the really early coin types fascinate me: Liberty Cap Half Cents and large cents, Flowing Hair silver coins, Bust gold coins, etc. The 1793 one-year type coppers - the earliest coins produced for circulation by the U.S. Mint - are especially intriguing to me. Perhaps one day I will be able to score myself a Chain cent, Wreath cent, or Liberty Cap Left Half Cent.