We seem to be stuck in this loop. "Best" drop, again, is subjective.
Ok, I'll stop playing grammar nazi now and offer up some advice.
I would like to start off by saying I haven't lowered my S197 yet, but I did own a 99 Cobra that I lowered "the right way".
What's the right way, you ask? Well, I can tell you what the "wrong" way is. By just installing springs only, or dare I say cutting coils on your stock springs.
The right way involves purchasing all the necessary parts to keep the geometry in alignment and handle the increased spring rates.
First you have to decide if you want to do a coilover conversion kit or stick with the standard strut/spring combo.
Then you'll want to consider things like:
struts
shocks
springs
caster camber plates
ball joint kit
bumpsteer kit
pandhard bar
rear LCA relocation brackets
I'm sure there is something else I'm missing off the top of my head....