Congratulation on your Insead admit. What a conflict of interest, one can almost assume that both programmes do this deliberately to manage their yields.
You can try to:
1) Ask LBS for early decision by telling your deposit at Insead is due and you wish to make a decision with LBS outcome. Some programmes are sympathetic
2) Ask Insead for defered deposit
IMHO, strategy and industry in South America would point to Insead in terms of placement, alumni network, classes. What Swiss uni did you go to, the federal techs or one of the Kanton unis?