My current travel setup is the XT1 with 18-135, 14, 35, and I just picked up the 27. On my last trip (Belgium & Netherlands) I mostly used the 18-135 and the 35 was my go to in museums and at night as well as the occasional portrait. I make a point of using the 14 a few times when I travel..great lens but I'm glad it's small as I couldn't justify lugging something larger around all day.
I'm looking forward to using the 27 on my next trip as my go to for street photos as I've found the 18-135 is just too big and the 35 (for me) a touch too tight for those situations.
Good luck with your choices and enjoy the trip! You're going to love Italy. The people, the sights, the landscape, the art, the food..all fantastic.