I do love most offal, apart from the aforementioned testicles and the Chinese speciality of "chicken butt"...
Byzantine nations seem to have a special talent to prepare offal, as well as Chinese, Japanese and Koreans.
Sometimes hard to choose if my favourite preparation is Turkish or possibly Korean. Or Xinjiang province in China, around halfway between those two great offal nations.
Turkish grilled heart is unbelievably good, as is Korean black pudding and cow stomach soup. As for liver, there I admit Italians do it better...China, of course, has always been an Empire of various cheap meats.
Ok, maybe the steamed pig head's soup at one of the Gwangju food market restaurant stalls in Korea is is my absolute favourite. Preferably evening time food and with some soju to wash it down...