For world time my favourite front and back is 5110/5130/5230. Front and functionality I do like the JLC geo and universal. The Vacheron, Glashutte and Breguet are both very nice, but a bit on the larger side and for the money I like the Patek world time. It’s a nice theme for a collection though. I’m sure there are a few notable others I’m not thinking of at the moment.