To me it boils down to a choice between do you want to minimize short term risk with possible greater long term expense (e.g. to move from M1 to M2 later), or do you want to avoid the upgrade cost.
M1 is going to be around for years - it's not going away. But the majority of core development effort is going into M2. There will be extensions at/near launch, but there are certainly more available for M1. Also, M2 is not launched yet! It is coming very soon, but if you want your store up by end of this year that is cutting it pretty fine if you want any extensions etc.
So it is not silly going with M1 if you want to reduce risk and need the site up fast; go with M2 if you are more concerned about being on the new platform to avoid upgrade costs later.
