Selecting Monte Carlo or Latin Hypercube sampling affects how random numbers are generated for individual assumptions.
In almost all cases, Latin Hypercube produces more accurate forecast statistics (especially the mean) given the same number of trials as Monte Carlo, because it is a more consistent sampling method. If you are primarily interested in the accuracy of the statistics, you should select Latin Hypercube as the sampling method in the Sampling tab of the Run Preferences dialog.
If you are primarily interested in evaluating how the spreadsheet model behaves under various "what-if" scenarios, you should select Monte Carlo as the sampling method. Monte Carlo produces assumptions with the most randomness and simulates real-life situations the best.