Ektachrome 100 Plus is a first-generation E-6 Ektachrome, which doesn't use T-Grain emulsion, and is a lot grainier than E100G or Elite Chrome 100.
I find that E100G is very neutral, with some of the saturation boost of slide film. Shadows can go blue, since they are lit by sky, which is blue (not white). E100GX had a warm color balance to counter that, but is discontinued. Elite Chrome is the consumer version of E100GX -- they probably aren't making any more, but there's plenty in inventory.
Astia is the lowest color saturation of all these films. Probably best for portraits.