They all do the same thing. MSD has the brand recognition and many additional ignition accessories. I chose the Crane HI-6 which includes the adjustable rev limiter built into the unit. No pills required (MSD system). Currently at Summit and Jegs the Crane system also includes a coil for something like $199. The 6AL is about $189 without coil. The Mallory VI does not have a rev limiter.
1966 Shelby Cobra Replica with a 1990 5.0L, GT-40P's, T-5, 3-link/PHB