The 2-1/1-3 + 12 stamina garden farming is for lower levels, when your girls are still unevolved or below lvl 20 evolved. It is the best way to get exp fast. Combined with having a decent exp ratio you will level fast and your girls will level faster as a result.
Once past that, 12-3 and 12-5 are your best choices because once you go past evolved lvl 20, the cost is going to pile up and you'll be coin starved unless you start doing the higher maps instead. The 50 stamina gardens are horrible for the records.
Now, for the whole 12-4 vs 12-3. Let's get this straight - 12-3 grants more coin, about the same seed, costs less and also has a way easier chances to get the chests. 12-4 is a... to describe it lightly: megafuckingrngpaininthearseoffuckingdoomanddestruc tionwithacherryonthetop.
Might have overdone that, but all in all 12-3 gives better in everything but exp ratio, and that ratio is a "magnificent" 0.2 per stamina.