Futari is great, but both Mushihime games has the worst aesthetic of any of the Cave shmups. Giant ugly insects....yay? The gameplay is very much there but I also like the gorgeous 2d side of Cave to compliment their great gameplay. Death Smiles offers cool looking sprites and really awesome bosses (EVIL COW) that I just don't get in Futari.
Plus I like that Death Smiles has more story inserted into the game (a nice cute story with multiple endings). And I like the soundtrack in DS a lot more than Mushihime. Plus since I suck at these games I like that Death Smiles is easy

Having multiple characters that all play different is nice too.
I mean the boss of Death Smiles is
TYRANNOSATANThat has more personality than any evil beattle or rocket ship.