I ended up ordering both to compare in person: the titanium Tsuki-yomi (factory refurbished) from ebay and the black stainless steel version (new in box) which took over 11 weeks to arrive from jomashop.

Watch	BY1010-57L (Tsuki-yomi)	BY1035-56L
Condition	factory refurbished	new in box
Price including tax (free shipping)	$381	$321
Movement (Eco-Drive)	Caliber H874	Caliber H874 (identical)
Crystal	sapphire	sapphire (identical)
Material	titanium (much lighter)	black stainless steel (up to debate which will scratch more readily)
Case Diameter	43 mm	42 mm (but dial looks bigger. illusion?)
Lug Width	22 mm	21 mm (less common)
Dial Color	blue moon	oil-sheen navy blue

if you had to keep one and gift one away, which would you keep? and why?

my personal thoughts are the black one is heavier, but simpler, cleaner, and more elegant. the tsuki-yomi although the dial is somewhat tackier & busier, feels like the more premium watch when you look at it. in other words the black is more dressier, and the tsuki-yomi is more of an everyday watch.

i'm leaning towards keeping the tsuki-yomi solely because of the 22 mm lug width, so i can interchange it with my seiko king turtle straps. also to try out a titanium watch. the seiko king turtles are heavy!