Best and Fastest way to Max Your 5's and 6's?

I have three 6 stars and a couple 5 stars, but after all this time, I've only managed to max my first 5 star and I got my first 6* in a trade already maxed.

So my question is whats the fastest and most efficient way to max out my cards? I already create feeders, but when and for what cards should I use them for?

Thank you!

Dunno about feeders as I tend to just use them on monsters or whenever we get an enhance boost from a panel event in which case I generally don't care on efficiency. Most of my exp comes from grinding quest 43-6 with 1 unit + max allies. This works fairly well time wise for me up to about lv 100-120 depending on my mood.

Or I grind exp on events like the one going now. I've been farming Barbara to cap alot of my cards as she awards over 65K exp with max allies deployed when you kill her. Most other training events seem to be great for exp also along with events that feature bosses like panel events or vs npc colosseum battles like the gifting event.

a part of what UkyoSonoda said, you can go grind the Training 26-5.

In that stage, you can loot 3* monster x1, 2* unit x1, 1* unit x2.

feed the 3* monster to level 11 with 2* unit x 6 + 1* unit x1

stock afew level 11 3* monster to feed your 5/6*.

PangCY provided a great tip. It is quest 26-5 though in case you are hunting for 25-6.

Just FYI, quest 45-6 is the latest quest with 5 allies and 2 of your units available, if you've reached quest 45 though
Good grinding