Manyu dailies are more reliable for getting manyus of 2 specified colors (getting manyus of that color AT ALL), but their XP/Gold/Seeds to stamina ratios are terrible. They're mostly useful if:
1) You have lots of excess stamina to burn and you're nearing level up
2) You REALLY need manyus of those two colors and don't really need the other 2 colors
3) You don't feel like "chancing it" with SG spawns (since those are random)
Ultimately, it's not recommended to farm them at low levels due to the fact they eat through your stamina REALLY quickly without much XP in return (80 stamina daily gives 160 XP, 50 gives 100, 25 gives 50) and you'd rather gain Commander levels to raise max stamina.
Recommended path:
1-3/2-1 spam + SGs until team is around level 30+
12-3 spam + SGs until you're satisfied with your girls' levels (12-3 can be cleared REALLY quickly compared to 12-5 and the 13 maps)
Alternate Path, requires strong helpers:
1-3/2-1 spam + SGs, pick your favorite girl that you have and pour ALL manyus of her color into her, powerleveling her to 30+
Ride helper squads through every maps until you reach 12-3
Spam 12-3 endlessly to generate SGs, putting ALL squads on the top left camp, bypassing the bottom and left sides of the maps for REALLY quick clears
Once you're happy with your squads' levels, go back and 3* all those maps you cheesed through with the helper squads