Defense debuff is the most powerful in the game, so the higher one has a bigger impact than attack stat ( see notes ).
But.
For titans, and triple bosses, normal/ matching/ tile/ physical damage is more important so either order is fine.
Notes
Click for notes
Using the 5* damage formula as we currently understand it
Color stacking
3x Scarlett color stacking
Evelyn
1 - 54% green defense debuff = 0.46
( Attack stat / ( Defense * 0.46 ) )^1.35
Factor out
( Attack stat / ( Defense ) )^1.35 * ( 1 / 0.46 )^1.35
Or
( 1 / 0.46 )^1.35= approximately 2.8528x damage next green tile or green tinted special attack
Buddy
versus
1 - 34% all defense debuff = 0.46
( 1 / 0.66 )^1.35= approximately 1.7523x damage next any attack
Comparison
2.8528 green debuff x 531 Buddy base attack stat ( without troops and emblems) = 1,514.8368 attack
1.7523 any debuff x 727 Evelyn base attack stat ( without troops and emblems)= 1,273.9221 attack
1,514.8368 / 1,273.9221 = 1.1891x more attack stat for the second attack if Evelyn then buddy
So to maximize the damage from the second attack, green defense debuff then all defense debuff.
FIN