They all exist in the fastest version. I tweaked the fastest version, saved the preset and copied the parameters from it to the forum. Only parameters which were changed from their default values get listed in the preset. It is the same situation every time when you tweak a shader and save the preset.
Really hard to tell, because some variants are here for less capable GPUs. Otherwise, all can do pretty well with most content. In general, the HD version is good for cores with higher native resolution input, standard and lite versions can do vertical content with MAME (TATE mode) and the NTSC version is special regarding image processing.
1080p displays are better off with less mask width, so it’s best you select the mask you prefer to look at this resolution. The best options are masks 6, 9 and 10 with mask zoom set to 0.0 (in other words, you don’t use mask zoom).
This option is a part of the Retroarch shader menu. It allows you to combine presets once you already loaded a shader preset. “Prepend” means you want the new selected preset to be before the current preset in the shader chain.