Some says that 90 degrees is enough other say that you must touch the floor and that is better as more muscles are involved.

IMHO 90 degress is better as when you are going below your back is not straight and that is risky.

What is your experience and opinion?

I do both, but with 90's I can use more weight, I pause for a second before coming back up and I'm sore the next few days.

ive always stuck with until my hams touch my calves - wouldnt ever go any further, it sounds too bad on the knees.

The trouble with going past 90 for me...it seems to put too much pressure on the knees. I know a guy that was huge when younger and well, he still isn't small lol, but he has trouble getting off a chair first thing in the morning from doing heavy squats when he was younger.

He likes to warn younger guys about this.

Maybe going to the floor is no problem, I can't say, but its something to think about.

Some sources say what I just said is BS, others agree. I found this a few minutes ago:

During the descent phase of any type of squat, leg press, or hack squat, do not allow the knees to extend beyond your toes. The further your knees travel over your feet, the greater the shearing forces on the patellar tendon and ligament in the knee.

Although many top bodybuilders advocate a very close stance for the purpose of isolating the outer quads, this is a myth, and it places you at risk, particularly since you'll have to use a lot of back to execute the lift, or (if you use heels) place great shear and compression on the knees, especially the posterior cruciate ligament which stabilizes the knee joint and limits rotation and hyperextension of the knee.

Always warm up thoroughly before squatting. Your muscles and other tissues of the knee joint LOVE warmth! Think of this analogy, cold taffy breaks, warm taffy doesn't. So warm up to prevent injuries

I use about 100 degrees however I think you must go down as long as your back is straight.