Best Bicep exercise?

Hi i was wondering what exercises target the bicep the most? I know preacher curls dont, why is this such a popular curl, the one where you put your arm on a slanted bench and curl up the dumbell?
Any thoughts? Also whats the difference when you do the alt curls and you turn your wrist all the way so the outside is facing forward when you are all the way at the bottem compared to you keeping the wrists parallel to your body at the bottem?

Preachers adjust the angle to isolate the biceps, you can use pinkies up or down to hit one head more than the other.  Can't cheat on this.
I like standing bar curls myself, its compound and you can cheat a bit to go heavier, and you can use a 45 lb bar in the squat rack, adjust the spot bars low and add plates - most gyms don't have too many bars ready set with weights, although mine does........my gym has dbs that are like 110 lbs each!!!

dbs? in my gym i used to go to i think it only went to 135lb dbs

I do 5 sets total for biceps because i take a long 2 min break inbtw sets and i do 10-12 reps and i also work my chest that day. So what exercises should i devote to these 5 biceps sets?

Im trying to target the forarms the L-E-A-S-T! because i do forearms on my back day. So what exercise targets the bicep the most and forearms the least? And  what angle for the preacher curls and how far down should i go? All the way?

Thanks alot!

PS - i heard ronnie coleman does one-arm cable curls, are these any good?

I thought preacher curls target the muscle right below the bicep? the Brachialis

anyone? When i do the preacher curls should i put my armpit on the top of the slant? Or is there different method for targeting the bicep more than the forarms?

try "preacher curls" the other side of the bench... resting your arm on the vertical board

I've had very stubborn biceps over the years.  I changed my routine up a year ago to dedicate a day to biceps & forearms, as well as cardio or abs depending on my schedule.  I've seen great results (for me) with the following excercises are varied with each work, however I often do 4 exercises of 4-5 sets each.
 
1) Barbell Curls 4-5 sets (6-10 reps)
2) Seated alternating DB curls 4 sets (8 reps)...I'll often do drops sets on my last two sets to really burn up my bi's.  I'll use 40lb. or 35lb DBs for 6 reps than drop to a 30 or 25lb DB for another 6-8 (or until failure).
3) Preacher Curls 4 sets (6-10 reps) -- Slow and in control, squeeze at the top.
4) One-arm Cable Curls 4 sets (8-10 reps) -- Again, slow and in control, really squeezing the bicep at the top of the movement.  I find these work better for me than concentration curls as I just don't feel anything with concentration curls.
5) Rope Hammer Curl 4 sets (6-10 reps) - Attach a rope to a lower cable pulley and perform hammer curls.
6) Incline DB Curls 4 sets (6-10 reps) - Same as seated just with an incline bench.
7) Squatting Cable Curls 4 sets (8-12 reps) - with a straight or shaped bar attached to a lower cable pulley sqaut down, place your elbows on each knee and curl the bar to your chest.
 
I hope this is helpful.

Thanks, yeah i think im going to do:
3 sets Straight bar Curls
1 set Vertical curls
1 set One arm Cable curls
I do 10-12 reps after a warmup, really slow, and 2 min rest inbetween
Thanks again for all the feedback

Best Bicep exercise?

all of them.  no one exercise is going to fullfill your bicep expectations.  its a combination of many things.   

My best results were with alternating dumbell curls.

which bicep exercises use the forearms the least?

Seated Curls, ones on the inside of the leg, imo.
Personnaly, i love preacher curls, there one of my favourites.
 
But there isn't a specific excersise that will be the *best* for your bis.

straight bar curls give me the biggest pump.

Im with them 2 ^^