I actually like a lot of theme songs for shows! I can't even name them all but, I like the ones for Kim Possible, Orphan Black, Full House, Friends, Heroes, Gravity Falls, Scrubs, Danny Phantom, Jimmy Neutron, Unbreakable Kimmy Schmidt, Gilmore Girls, Noragami etc. The ones without words I like because they just fit the tone of the show really well, and are lovely in their own right. The ones that are cartoons are just fun to sing along to. It's a combination of nostalgia, love for the show, catchiness and just being good songs in general that makes me love them.
Also, honorable mention of course goes to Too Many Cooks. The best theme song for a non-existent show ever.