I meet halfway and farm 10-3 most of the time. It gives 507 stamina points, about 500-600 normal gacha seeds, and triggers the SG for 50 stamina quite often. You can get lvl 100 manyus in that SG too.
12-3 is easier to collect all the treasure so better amp odds slightly
12-5 is more gold/seeds/xp per stamina I think
1-3 is fine if you want low level manys
I find the secret garden rate is about the same between 12-5 and 12-3. 12-3 takes less stamina and is better if you're only interested in manyus but 12-5 gives a lot more gold and seeds, and a higher level raid boss.
As for farming 12-5, I've found one really strong squad will go a lot further than several fairly strong squads. If the squad doesn't reach a certain level of power it will just be destroyed or crippled by the threestepper nodes. On the other hand one 100k+ team with Edelweiss and Lavender for sustainability and a slice type or 2 can clear the map on its own.
FKG ID: 781816890
Osawari Island: 41IHR698M3HLETVI3O3JP
In the beginning, while I was still short on AP I wanted to play the heck out of this game yet could not, since just two 50 AP mission pretty much made me stop playing for half the day.
Now I have almost 280 Stamina and units strong enough to clear the event and farming mission so taking it easy is how its best done.
After all - what else can you do with a game that limits your playtime ?
Get in, play till you exhaust all your stamina, and then go do something else for the day. Log in later and mash out rest of the daily. Done
Once you "absorb the fact" (not just understand, you actually have to get in the pace of it) that the "progress" in this game (since there is no real story to progress) is paced around the events, and thus its rather slow (they change every 2 weeks after all), the nervous "hustle" compeling you to "do something" in the game, you feel at the moment will gradually fall off, and you´ll be able to enjoy if for what it is.
At least thats how it feels for my when I play games of this (browser) type.