Which camera should I bring with me on my trip to Central/Eastern Europe?

I'm going on a trip to Central/Eastern Europe in a few weeks, and I'm facing a dilemma over which camera I should bring. I have a Nikon D90 and a Nikon 1 S1. I'm not a professional photography, but it is an avid hobby of mine. I usually take photos with my iPhone. I want nice pictures for this trip but I also don't want to lug around and be so invested in being alert over the D90 that I won't be enjoying the trip. I haven't practiced all too much with the D90, but I know enough to take OK pictures. I don't like the quality of the S1 very much, but it's easy to use and it's much lighter. This trip is one of those "once in a lifetime" trips. I want to make sure I have good pictures, but I don't want to have to compromise too much comfort for it. Thoughts?

I took my D90 on our once in a lifetime trip to Paris last year. I have no regrets for the weight. And Paris is rife with pickpockets and thieves, so just keeping it always around my neck seemed to be all the security I needed. Do practice with it as much as you can before you go.

Take the S1. Infinitely better pictures than from the iPhone and much less weight than the D90. Just remember to keep it with you all the time.