I'd stick to Kathamandu. That name sounds so exotic and a lot fo people say " I want to go to Kathmandu, Nepal at least once in my lifetime". Even for me, being a Nepali and a native of Kathmandu, Kantipur doesn't do the same thing as Kathmandu. When I see the name "Kathmandu" , I feel something inside and connects me with Nepal, for e.g., appearence of word Kathmandu in CNN, BBC both online and TV, Time, Newsweek, my airline ticket to Nepal, passport; conversation with fellow Nepali or foreigners etc. etc. I want to stick to Kathmandu.