I truly do not know, and this may be a highly personal response, unless, of course, you work for Lonely Planet. They visit quite a lot.
I liked Kawaii, in the Island of Hawaii. Nice and long beautiful trail. I liked the Anapurna trail in Nepal. Extremely beautiful trail and Poon Hill, up some 3000 metres plus, I believe, was rather like visiting Heaven.
Anchor Watt in Cambodia is not so much a trail but here you will see some of the most astonishing ruins. Machu Pichu is outstanding and going up the mountain in Bali, is quite touching.
In my own England, I have gone to The Yorkshire Dales, walked through forest trails, along Glastonbury and beyond. I have done the Scottish Highlands and been up mountains there too.
Yes, I know that I have not given you a definitive. I have done the Swiss Alps and gone 4000 metres up Kilimanjaro. It is very beautiful. Too much more to tell, but I do remember walking through my grandfather's lands in the tiny country of Grenada with much Love. Up to and looking down from Mt Beauveau in France is a sight to behold.