I am going to go with the MM ones because I plan on using their products to entirely re-do my rear suspension, i.e. the LCA's, panhard bar, and torque arm. so I want everything from the same MFR to ensure compatability.
I don't think you can go wrong with either. I have MM LCA and Steeda uppers and both are nice pieces. If you want to use the same brand for both upper and lower you will need to go with Steeda. I don't think MM makes and upper. They recommend the FRPP UCA on their website.
I have the Steeda Aluminum uppers and lowers. I really like um. Major difference in weight between the stock and the aluminums. The aluminum alloy used in these arms is actually stronger than the steal ones.