Leasing is a terrible idea if you cannot write off the monthly expenses from your taxes. Leasing makes it so that your car does not become part of your assets and therefore it is non-taxable. The way I see it, is that leasing is only there for people to take advantage of the tax write offs.(otherwise you are throwing away hard earned money) Financing is for people who want to keep that car long term but would rather pay for it slowly rather than lump sum if they don't have the cash.
I would suggest that if you ultimately want a M brand in 2-3 years. To buy a car that will only run for the next 2-3 years into the ground. By that time you will have saved up enough to finance or buy your dream car. Meanwhile not wasting your $$$ by paying interest to the dealership for no reason. Save those monthly payments and interest and fully load that M car.