I collected as a kid,
inherited the collections of my grandfathers and parents, then put the hobby aside. In the last few years I have rediscovered it, realizing that it is not some trivial pursuit but rather a deeply meaningful and nourishing activity.
I specialize in France up to the 1970s and Germany until about 1950. Also I am looking for at least one stamp from each stamp-producing entity. I am especially enthusiastic about colonies, dead countries, and occupation zones. Danzig, Hapsburg-era Bosnia, and Mucha-designed Czechosolovakia are among my current foci. I get carried away with engraved stamps from that period between the 1890s and WWII where the imagery is especially compelling, evocative, and subtly propagandistic. Though I generally avoid topical CTOs I have a weakness for Bhutan, having recently visited there, splurging at the philatelic desk of the Thimpu post office.
I do have a few small topical collections though. One consists of carnivorous plants but only if they actually grow in the country issuing the stamps. Another is of Vikings and Norse mythology. Actually it was a websearch for that topic that led me to this here community.