Help with Crossover design for Portable Stereo?

[Nathan B]

I am designing a portable stereo system, and I want to design some crossovers for my speakers. I have a pair of 4ohm 6" celestion Ditton midranges and I am going to buy a pair of 4ohm Vifa XT25-somethings. Can someone explain to me what all the different crossover types (Butterworth, Solen Split, etc) are and which one I should use to design my crossover? The website I am using to calculate the crossovers is http://www.diyaudioandvideo.com/Calculator/XOver/