I have the 70-200 f/4 IS. I chose the 70-200 mainly because I take most of my pictures while hiking and the difference in weight isn't negligible when you carry the lens (and a bunch of other things of course) during the whole day. The other argument in his favor was the slightly less expensive price. The obvious advantage of the 70-300 is the focal length. From what I read, there are not a lot of differences in terms of performance (IQ and AF), so in the end in depends on what you do during your travels, what you like to take pictures of and how much weight you want to carry with you.

Both are great lenses and I don't think you'll be disappointed by any of the two. It would be nice to be able to see them and to try them on your camera to feel the difference between 200 and 300mm though.