Best use of Quest Experience

I'm grinding for souls right now and was wondering something about experience gain.

I'm leveling a 7* right now. Is it better too...

1. Just deploy the 7* and gain the 675 exp from the quest.
or
2. Deploy a 2*, 3* or 4* unit to level them and then feed them to my 7*.

Which method gets me the most out of my 675 exp?



Also, i forget often, what is the best level to raise feeders to for max exp gain.
I thought it was 2* lv4, 3* lv8, 4* lv12.

Always level the unit directly unless it's a monster.

The 2* breakeven point is lvl 4 (the amount of experience put in = the amount of experience it's worth when enhancing). So I wouldn't bother with 2*'s.

Using a bunch of 4*'s might be a good idea since it'll cut down on enhancing costs and we all got hundreds from the those ticket give aways before summer. The breakeven point for 4*'s is early lvl 20's depending on your skills and if you have the type bonus.