After Effects: Images on whole pixel still blurry edges
So, I figured it out by myself. The problem was the anchorpoint. My images were on even pixels but the anchorpoint was odd.

So the solution is to use following expressions:

// Position
newX = Math.round(transform.position[0]);
newY = Math.round(transform.position[1]);
[newX, newY]

// Anchorpoint
newX = Math.round(transform.anchorpoint[0]);
newY = Math.round(transform.anchorpoint[1]);
[newX, newY]


UPDATE 2

Since I use this expression everytime now I am animating motion graphics, I thought it would be cool to make an actual after effects script of it. You can purchase it here:
FIXL -Snap Layers to Pixel

UPDATE

When you try to animate layers with these expressions, it comes to rough animations. That's why I wrote a new expression that only applies if a keyframe is set. So its safe that whenever an image or layer is resting on the same position for a longer time, it will stay on even pixels.

Add this Expression to the position property of your layer:

n = transform.position.numKeys
t = time;
timeOfKeyframe = null;

for(i=1; i &lt;= n; i++){
    if ( t == transform.position.key(i).time ){
        timeOfKeyframe = transform.position.key(i).time;
    }
    else{
        value;
    }
}

if (t == timeOfKeyframe) {
    keyValue = transform.position.valueAtTime(timeOfKeyframe);
    roundedValue = [Math.round(keyValue[0]),Math.round(keyValue[1])];
}
else{
    value;
}