I use all three and recommend a 28mm/50mm combination. You will find that those two will cover most eventualities. I took a 135mm on a trip to Madrid a few years ago and used it, but not much. While I like a 28/50 combo, I also find that 35/75 also works very well. I was recently in Germany with a 24/35/75 combo and that covered absolutely everything. In the future you may want to consider a 21/28/50 kit. Have a wonderful trip and post photos when you get back!
