Pretty sure the only difference in those two models is capacity - controller and type of flash is the exact same. I personally would opt for 256GB.
There is also an M4 being sold with a data transfer kit, this one has a different model number/SKU than the other retail one, but it is the same drive part as far as I can tell.
This is the one I got.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820148443