In terms of mechanical integrity and reliability there is no difference. Some MM cartridges have replaceable styluses where this is impossible with MC cartridges.
MC cartridges offer a level of performance that is definitively superior to MM cartridges but at 4 to 5 times the expense. The difference in soundstage and imaging is quite profound. It is difficult but not impossible for a MC cartridge to match the dynamics of a MM cartridge and the MC cartridges that do it are very expensive. The only alternative is going digital.