Although I naturally lean in the direction of more power, as Murphy's law would have it something will go wrong. (usually in the middle of nowhere) and since the quality is the same, better to have something that can be fixed locally and be able to keep rolling down the road. So by a slender margin I'll go with the 200L. Btw, have you considered taking some critical parts with you?
This link is on the differences between a Vespa GT200 carbureted model and the GTS250. (not exactly the same, but gives you a rough idea.)
http://modernvespa.com/forum/topic66272