I have and use both GE1 black (GE312A), and ASI black. Hundreds of caulking tubes of each.
GE is smooth, "soft", flows well, dry to the touch in 24 hours (up to 1/2" thick), but thicker sections take a week to fully cure. Once solid, is a soft durometer, and does not attach parts well. Great for fillers, and textures. Put some alcohol on your fingers and your can work it into really nice "cake frosting" shapes.
ASI is sticky, does not flow as well, and drys completely solid in 24 hours (up to 1/2" thick). It is a harder durometer, more like rubber, and attaches parts in a very very strong way. Not good for fillers and textures, even with alcohol. Twice the price of GE1, but is mandatory for structural components such as building a tank.