It isn't a question you can answer with a short answer, and the better of it, is that you don't have to; you can change. Right now, after our last game ( 3 of a party of five killed and myself blinded by Dansart Forces), i am thinking of giving a bit of ground between me and Dansart; we believe Osaran will like to continue his vengance against us. So, this is what i like of Shadow World and our way of playing. I can decide to change what we are doing, and go to Emer to see another adventures. This feeling that i love that i can really move my way, and not only drive through the GM's encased highway.
Returning to the esence of the question, Emer for represent somehow the Wild West, more games changing totally from town to town, with each country has their particular culture, troubles and laws. Jaiman is more a kind of Europe, too dominated by Rhakhaan and the Crowns, yes sure you can play in Saralis, Urulan or the adventure that is on the Guild Aventurer, but sometimes this themes will be in the game.
I had played more in Jaiman , but i like both. Right now i will say Emer is best, because is bigger but problably most because i had played too much in Jaiman lately and i like to change.