Many great discussions are taking place about the future of the Multidimensional mode for the Analysis Services. It is very clear where the majority of the investment went for the 2012 version (hint… think rows and columns and not multidimensional). At the same time, one might argue that the traditional or Multidimensional set of features is already so robust that it does not require any additional $$$ to gain any additional market share. Microsoft managed to eek out almost 30 pages worth of analysis on which way is better here.
My personal advice would be to do the following, see if tabular mode will support the requirements first and if it does, do not hesitate and go with that. Otherwise, reluctantly choose the Multidimensional mode. I am a huge fan of the traditional model, but PowerView does not work with it, which makes it difficult to recommend by default anymore.
Some of the big No-Nos for the tabular mode are very large data volumes, complex calculations, write back, parent/child hierarchies, many to many and reference relationships, drillthroughs, aggregations, sets and semi-additive measures.