Re: guitar design for drop d?
Depends on your baseline reference, I suppose. Collective Soul did well enough with a Les Paul in drop D for Shine. EVH did well enough with a Strat in drop D for Unchained, as did Lynch, DeMartini, et al.
Type O Negative did well with Strat-shapes for baritone stuff.
Iommi didn't do too bad with a P90'd SG going as low as C# using 9s.
As with everything else, "best" is always going to be subjective.
However, let's assume you want a specific voicing without external EQing other than for basic need - overall level boosting for solos and/or feedback notching.
You've got to consider body shape. Strats and Les Pauls are 60-year-old standards, largely due to their comfortable fit while strapped on and their balanced tone - not overly prominent in either of the 3 main EQ bands.
Then you've got Vs and Explorers which tend to focus on certain frequency ranges, notably the mid area.
Then of course you've got the tonal qualities of various woods - bassy, bright, middy, etc.
A mahogany Explorer-shape (Star, Warrior, etc) is going to have a distinctive low-mid punch, while the same shape in alder is going to have a more mid-high bite.
Same with a V, though it's going to be focused more in the upper end of the mids into the low-highs.