My best advice is, if you're not sure whether to lease or buy, your best option is to buy. Buy/finance is usually what's best for most everyone. IMO leasing is only good for a small percentage of people, such as those who are self employed and can write off a huge chunk of the lease payments for tax savings. Now there are those who lease because maybe they can't afford the payments of a buying/finance plan, and try to get into the most car for the least amount of monthy and are stuck to the mileage. There are those who are absolutely sure that they change cars every few years so leasing provides the least hassle in changing cars, but they still have to abide by the mileage rules.
If you're not sure whether or not you'll change cars, just buy, don't lease. That was my scenario and I'm totally glad I chose to buy. If, and a big IF I do decide I want to change cars a few years down the road I can decide to sell it then and get good money for my car. BMWs right now have really good resale values. But chances are I'll be keeping my car 5+ years.