This is a good question.
What it comes down to is HDMI and DisplayPort are both digital. Although they are different standards you should get the exact same image through these ports if you are using identical monitors.
However VGA is analouge. If you recall the old analouge TV stations these would often be more subject to ghosting, fuzziness and interferance than digital, and it’s the exact same thing at play with VGA. You may get some better results with a higher quality cable but it will never look the same as VGA.
Most video cards these days will have just digital outputs and if its any sort of gaming card I’d expect you to have maybe 2 or 3 DisplayPort connections and perhaps the same amount of HDMIs.
Do you have any spare digital ports rather than using the VGA cable? This should help with the picture. If you are not using identical monitors then you won’t see the exact same picture. I have a dual monitor setup on my own desktop and even though the monitors are the same model there is an ever so slight difference as I bought the second one at a different time - it can be hard to get it to match exactly so I wouldn’t chase this too much personally.
