I dont know why anyone would go with a lease if its MORE expensive than buying (unless you have negative equity from a prior vehicle). The whole point of a lease is supposed to be that you make much smaller monthly payments than a purchase on a much nicer car, while at the sametime maintaing full warranty coverage through the entire period of the term.
HOWEVER, lease popularity has really dropped off over the past few years and rates (i.e. the Money Factor in a lease) are not as good as they used to be due to declining residuals. I dont know what you have heard about BMW reliability but since this isnt an american car, and the depreciation isnt nearly as bad as one, I would definitely choose purchase over lease here especially if the lease is MORE expensive.