These are two heavy hitters, and both are improved greatly by adding about 1mL of water to help open the flavors!
I chose the ECBP on my shelf that had the closest proof to the Jack.

Jack Daniel’s) 
-The nose starts with strong ethanol, and then oak, burnt smoky sugar, and vanilla. Also a hint of mint, and leather.
-The palate opens hot and spicy, with black pepper and cinnamon. Then the flavors of oak, vanilla, and brown sugar take over.
-the finish is fairly long, and is also spicy and oaky, with some molasses sweetness as it fades.
Overall this is an excellent, powerful whiskey that sweetens with about 1mL of water. It has classic whiskey flavors but is a little heavy on the spice.

Elijah Craig)
-The nose is intensely aromatic and complex. There is an initial hint of musty-sour-funk that then reveals oak char and roasted peanuts. Then the strong caramel/vanilla notes take over along with some allspice, and a bit of leather and cherry.
- The palate starts out with a thick, oily mouthfeel, and includes strong caramel, brown sugar, vanilla, and dark cherries, along with some salted peanuts, and allspice.
- The finish is long and sweet, with caramel corn, some black pepper spice, and some slightly drying oak tannins.
Overall this is an amazingly complex, powerful, flavorful pour. Going back to the B518, I was surprised how close it is to the B520! The only real difference is slightly less sweetness.

VERDICT) Fancy Glencairn chose to carry the fancier bottle today, and she learned a valuable lesson about judging a whiskey by it’s bottle!
While these are both outstanding, the ECBP is the clear winner. It just is more complex, more flavorful, and more interesting. I will always have a bottle of JDSBBP on my shelf, but my heart belongs to ECBP!