Specification Comparisons
Cover finishes
Matte vs. Glossy
Both services offer matte and glossy for book covers. In this example the matte finish is produced by IngramSpark and the glossy finish is produced by Amazon KDP.

Hardcovers
IngramSpark vs. Amazon KDP
IngramSpark hardcovers are definitely more costly to produce than Amazon, so naturally I need to inspect just what we're paying for.
Verdict: IngramSpark wins here. Even though both are case laminate (colour laminated cover glued to boards), IngramSpark's boards looks and feels higher quality (and SO nice to hold *dreamy sigh*). Amazon's is not bad, the board just feels a taaaad thinner.
Paperback
via Amazon KDP only
I didn't explore paperback via IngramSpark because the cost and quality of Amazon KDP (not to mention the unbeatable speedy shipping) is already very good. I mean... we get perfect bindings here!!
Verdict: Amazon KDP wins.
(side note: you see how much light is reflecting off the glossy cover spine? That's why I won't gloss.)
Hardcover vs. Paperback
Just sharing photos between the two!
Note: only hardcovers has the Fishy Design Studio imprint because it's via the registered ISBN/self-publishing route and everything (rather than the one-stop-shop through Amazon). So official-looking eeeeekk!!!
Ink Qualities
Premium Colour vs. Standard Colour
There are two different choices of coloured ink: premium and standard. Both services suggest that any books with lots of photos or illustrations (such as cookbooks, photography showcase and the likes) should choose premium ink for vibrancy. Of course, that means it hikes up the production cost. Premium is naturally the best option, but I was curious just how much "lesser" standard ink really is.
Verdict: Okay fine, premium ink wins. It really is more vibrant that pops more. It wouldn't do the drawings justice if I opt for standard and it'll ruin the experience.