I did some testing:


10x stage 12-3, bonus stage(80 stamina) and boss.

Finishing Stage 12-3 have around 40% chance of finding a L58 boss and 40% chance of finding a bonus stage
So 10x 12-3 give 4x bosses and 4x Bonus stage (80 stamina)

Total stamina cost 10 * 35 + 4 * 80 = 670 Stamina
Coins 10 * 3171 + 4* 8032 = 63838 Coins
Seed 10 * 564 + 4 * 690 = 8400 Steed
Exp 10 * 473 + 4* 160 = 5370 Exp
** girls 10 * 4.8 = 48 ** Girls (250 coins each)
* gift 10 * 0.2 = 2 * gift
*-upgrade 4 * 0 = 0.00 * upgrade (1080 girl exp each)
**-upgrade 4 * 2.66 = 10.67 ** upgrade (2700 girl exp each)
***-upgrade 4 * 0.66 = 2.67 *** upgrate (7200 girl exp each)
**-Item seed 4 * 72 = 288 ** Item seed

The 8400 seeds gives:
*-upgrade 84 * 2.4% = 2.0 * upgrade (1080 girl exp each)
**-girls 84 * 92% = 77.3 ** girls (250 coins each)
***-girls 84 * 5.3% = 4.5 *** girls ( 270 girl exp each)
****-girls 84 * 0.3% = 0.3 **** girls (360 girl exp each)

I sell all *2 girl for 250 coins, upgrade cost 4000 coins per girl used.

Net for 10x 12-3, bonus stage (80 stamina) and boss.
Stamina cost: 670
Coins: 14946
Girl exp: 51470
Exp 5370
*-Item seed: 0
**-Item seed: 288

12-3 per stamina point used:
Coins: 22.31
Girl exp: 76.82
Exp: 8.01
*-Item seed: 0
**-Item seed: 0.43

Same analysis for 12-1 gives:

12-1 per stamina point used:
Coins: 25.44
Girl exp: 78.99
Exp: 7.74
*-Item seed: 0
**-Item seed: 0.41

12-1 gives +2.8% more girl exp but 3.4% less exp and 4.1% less seeds than 12-3.
I cant say which is better 12-1 or 12-3 they as very much alike.

************************************************** ************************************************** ****************

2-1 per stamina point used:
Coins: -53.64
Girl Exp: 110.57
Exp: 11.92
*-Item seed: 0.83
**-Item seed: 0.00

2-1 gives 50% more exp and 50% more girl exp than 12-1 or 12-3.
It gives a bit fewer coins.
Stage 2-1 gives *-item seeds while 12-1 give **-item seeds.
If item seeds are used for upgrading 2-1 are better because 2-1 give twice as many seeds.

Conclusion: 2-1 are far better (50% better) than 12-1 and 12-3 per stamina point spend.
Main reason is: The 80-stamina-bonus-stage only give 3 time more girl exp than 12-stamina-bonus-stage but cost 6 times more stamina.

Only advantage of stages 12-1 and 12-3 are that they give 3 times more ****-girls per stamina spend than 2-1.