I have 12lb mono and 20lb braid (8lb equiv). I want to teach a few people how to cast, but i dont know which to put on. Does braid backlash more if they dont thumb the spool, i'd think not since it lays flat. But i don't know. Which should i spool up with?

Mono, it's cheaper. 

I don't really mind the price lol. Just whichever one backlashes less so they don't give up as quick. Here's links to the line I have

Berkley Fireline Fused Original 20lb

http://www.berkley-fishing.com/products/line/superline/fireline-fused-original

Trilene Big Game 12lb

http://www.berkley-fishing.com/products/line/960

I think mono backlashes more, but braid is easier to pick the birdnests out of

Ok, so if braid is easier to get the backlashes out of and doesnt get damaged or kinked from them and doesn't backlash as much (probably due to no memory) my next question is, should i bring them to the water or use it in the back yard? Will the line fray from repeated drags across the grass or should it be fine? I dont want to throw 20$ worth of braid away, but i also don't want them to get frustrated.

I would bring them to the water if possible. No point in fishing in the grass if you can be on the water. Also, grass isn't hard or rough enough to cause the line to get beat up at all

I used to practice in the back yard with a plug or beat up lure with no hook. Figured i'd try and do the same for them if its easier.

I find braid is easier "When your thumb starts to dumb" and especially for first time casters, when price is not an issue. And no memory lets me sometimes cast not even touching the spool. IDK why but I just cant use mono on baitcasting. Something about it makes me wanna scream because I have to chainsaw my line off. And water will always be better for practicing to "thumb" your baitcaster because your line will be wet, letting it slip under your thumb. And hell, maybe he'll catch a fish while practicing  8-) Also don't let him tie on anything less than 1/4 ounce at first 

Many love braid, but as one who hates it, I would recommend a soft mono like Berkley XL. It has little memory and casts great. Just my $.02

It is also inexpensive. 8-)

Does the diameter difference between the 20lb braid which is actually 8lb mono and the 12lb they suggested for my accurist make a difference in casting? I bought 12lb braid which i think is like 4lb mono when i first got it and kept having an issue with it snapping off and laying over itself. My spool has holes drilled in it, but not all the way through. Should that be good enough to hold it or do i need backing?

I would go with either 40-65# braid, 20 will dig in the spool a lot easier and cause break offs....  I use 65 personally... 

Since we're talking about beginners here, generally speaking the thinner the diameter the line, the harder it's going to be for them to learn on.  It spells trouble for beginners to learn with anything less than 8# mono's equivalent diamter, and even this could be a challenge for them.

Choose a mono from 10-14 test for them to learn on and they should learn just fine.  In addition, it is also the more economical. Take this as someone who spooled up 20# braid on his first lp casting reel learning solo. That was the fastest $12 I ever spent on line.  One cast, one major bird's nest that had to be cut off.

Then, as they gain more experience, they can acclimate themselve to lines of thinner diameter, which I happen to prefer when the cover permits.

With regard to which backlashes more, I would say the one with the thinner diameter, without the proper training. It doesn't matter the line type, but its diameter.

Yeah, I was eventually planning on picking up some #55 braid, but my grandfather was kind and went out and bought some for me without me knowing lol. So i have what i have. So you guys think it will lay into itself and be a waste on my baitcaster?

My Berkley Big Game #12 i use on my baitcaster right now has an average diameter of 0.36mm and the #20 braid i just got it 0.30mm. Is that difference big enough to cause issues? I converted the big game over to mm because it's 0.014 inches, which equates to 0.36mm :-).

Use the 12 lb mono.  it's better for a number of reasons. And set up the baitcaster for that it won't backlash easily, if at all. that way they only have to worry about putting their thumb on the spool right before the lure hits the water.  As they start to get familiar with things you can loosen up the reels so that their casts begin to go farther.And if you can do it in water you will be better off, because they can see the lure hit the water more easily than hitting the ground. And if they can't tell when it's going to hit the ground, you will be picking out birdnests constantly! I taught both of my sons without many issues, and without too much line sacrificed. Of course, the first time they try it when they are actually fishing they forget everything you have taught them, and they backlash a few times, until they settle down. Good luck, have fun, and try to be patient!

I would do really heavy (65 lb +) braid, or like 10 lb XL. Just what I would do, though.

Thanks guys, i think i'm going to go with the braid. Started another thread specifically for the line size. We'll see where that goes. This forum's awesome and patient :-)

I would do 20lb XL...