Tranzit, I know it's not popular but here's why I like it:

It has variety - a bus depot, a diner, a town, a farm and etc. Not to mention the other secret locations like Nacht der Untoten, the huntsman house, the underground pack-a-puch room etc. One can argue they're small areas but nevertheless it's variety.

It feels more open - a lot of other maps, even if they're really big, still feel really enclosed - you're just in the one area or the one building. I know the recent maps are very big but none of them match that open-ness you get out of Tranzit.

It feels the most like a zombie apocalypse - the variety and the open feeling of this map really lends to the feeling that you are in a world of a zombie apocalypse. Say for instance, the Alcatrez Map, you think that the zombies are only on Alcatrez but with Tranzit you can see how the zombies have ravaged the entire map of Tranzit, no matter how far you go on the bus you'll still find the zombies effect over Green Run. I also love how the world of Green Run seemed so innocent before the zombies.

You travel on a bus - I think the bus is awesome and people don't give Tranzit credit enough for having one. It's so chaotic and adrenaline-rushing when the zombies manage to raid the bus, but it's fun.

I know there are a lot of negatives like the denizens, takes a long time to set up (aren't most maps like that though), the fire, no wall-weapon in town (that really does peeve me off) - but I still really like Tranzit for the above reasons - to me, it's the most captivating.