You should choose your system based on the lenses you think you may need. For instance, do you prefer an all-in-one zoom lens? Do you want a street shooting pancake prime? Do you want a long range telephoto lens for bird watching? Do you like taking photos of bugs? These are important start points.
Based on your lens requirements, you can check the existing camera systems for lens availability, quality and cost. Read lens reviews. Choose the system first and then the camera body. The body price of any MILC (or DSLR) is usually much less compared to the prices of lenses over a long period of time.
Even if a lens system does not have the lens you are looking for it may be possible to use a lens meant for another system with an adapter on the camera body. Many of the MILC camera systems gained popularity because DSLR system owners could continue to use their lenses on the new MILC bodies. For instance Olympus DSLR lenses work on Olympus MILC cameras through an adapter like this one: http://www.amazon.com/dp/B002CGSYMQ?...tag=ii3plht-20