low pass filter with minimal ringing
Generally the amount of ringing that you get is a function of the steepness of the filter in the frequency domain, regardless of filter type. 
At the same steepness an Elliptic will require a lower order but will have pretty much the same ringing as a Butterworth. 

Choosing between a linear phase or minimum phase will change the character but not the extent of the ringing. 

No matter how you slice it, a square wave contains a lot of high frequencies and once you filter those out, it's not a square wave any more.