Maybe this will help. Blue is tier 2 fake, red tier 3. The numbers are reset bonus/1000. Lola is 500 only when complete. Last checked maybe a month ago. Game gets patched now and then :-)
But basically, reset if you have to wait too long for money/skills.
Increment Increment Increas to last girl 1 2 3 4 5 6 7 8 9 10 Total Cherry 8 14 22 30 38 46 54 62 70 78 86 500 Sanshi 16 8 28 44 60 76 92 108 124 140 156 172 1000 Ice 24 8 42 66 90 114 138 162 186 210 234 258 1500 Geeky 32 8 56 88 120 152 184 216 248 280 312 344 2000 Dora 40 8 70 110 150 190 230 270 310 350 390 430 2500 Frecly 64 24 112 176 240 304 368 432 496 560 624 688 4000 Pantress 96 32 168 264 360 456 552 648 744 840 936 1032 6000 Victoria 128 32 224 352 480 608 736 864 992 1120 1248 1376 8000 Cindy 144 16 252 396 540 684 828 972 1116 1260 1404 1548 9000 Emma 176 32 308 484 660 836 1012 1188 1364 1540 1716 1892 11000 Indira 192 16 336 528 720 912 1104 1296 1488 1680 1872 2064 12000
And you will have to balance resets with training time. Make sure to unlock your hit girl b4 logging off and send her to train. As of now your Total bonus gives not the slightest help in challenge. So just unlocking your highest girl and training her and not resetting would be a valid strategy. I tried to change my tier 1 hit girl to a tier 2 girl, but no way. It would probabyl take months to reach her. Sure, the tier 2 girl could reach a way higher stamina and train more stats, but as I just checked, double stamina is not double stat from training. Maybe I try again with a tier 3 girl and parallel train both the new girl and the current hit girl.