Classical. There's always something new to discover. Easily the most radical and creative genre. Plus a few hundred years of composition. Classical kicks ass.
Next is jazz. Not as deep as classical, but loads of innovation over decades. Plenty to discover and love.
Country is a lot like jazz and might be the most underappreciated genre. Too many overlook it, but you'll find excellent compositions and musicians all over. I wish more people would listen to country - it is wonderful.
I also have a love for alternative rock from the 1980s through the mid-1990s. I grew up with this music. Some nostalgia, but there was innovation, too. In some ways, the New Wave reminds me of early rock from the 1950s, which I also like.
I don't have much depth in it (yet), but World Music is great, too. Lots and lots of subgenres. One I love is Afropop. It always makes me happy.