X was always going to be for Xi'an. Not too much pondering required for that one. I'm not certain I've even heard of another X city - are there some in Mexico? I think so, but none that anyone has ever recommended to me.
Despite that, I did like Xi'an. I went for the pottery soldiers, and came away just really liking the city. The snow was crazy, the clearance crazier, the dumplings were everywhere and you could cycle on the city walls. Where else can you do that? Try and do that in Chester and you'll be tsked right off.
Plus Xi'an is somewhat immortalised for being laughed at by locals for eating weird meat off a barbecue. I think it was a ram's personal area. And if eating sheep penis doesn't make you like a city what does?
And yes, you're right. I have started at this end of the alphabet because I thought it would be easier. Umming and Aahing because I couldn't decide between Arequipa and Asuncion (bad example, my experience of Arequipa was eating Domino's whilst racked with food poisoning whereas Asuncion was all about karaoke and pirate bar. Asuncion wins hands down - but you know what I mean), whereas this end of the alphabet the cities are fewer and further between. Or all in China. Either way:
X is for Xi'an.