In Illustrator/CS6, I've drawn a diagonal line with my pen tool and then changed the stroke to 14. The line looks pixelated. Onscreen. Immediately...before I export it to any other type of file.
In Preferences: I have "Anti-aliased Artwork" checked.
Under Rasterize I've tried a few settings, including 300dpi.
I've tried what older posts recommend, to no avail:
I had to laugh when older posts suggested the person with the pixelated lines was just nit-picky. I'm nit-picky too! And so is my client, who just wants a straight, clean diagonal line.
The odd thing is that I've exported this pixelated line as an svg...scaled it and printed it 6-feet tall...and it looked great. But onscreen - in my .ai file and in the various forms you can export it to for web use - it looks rough.
Here's a screen shot, but it's hard to tell from it unless you zoom in. It is not hard to tell on my .ai file, though.
Your monitor has to use pixels to display anything. No matter how straight and precise the vector path is, the screen will always show pixels. The greater the pixel density of your monitor the less noticable pixel edges are. Until there's some massive innovation in display technology, this is merely how things work. You should trust that vector is vector and will be output as smooth, straight paths. You could always upgrade to a 4k display if it bothers you that much. It won't remove the issue entirely, but will greatly improve the pixel display of the monitor.