I would say the right one is a forgery l am no expert but I don't think I have ever seen one that well centered, also the letters on the legend seem a bit soft and to thin.
I vote for the one on the right as well. Something 'undefinable' about it does not seem right. Could be the legends, the centering, the size of the flan, also the style and size of the bust. Not quite right.
I love this game, @PMONNEY. The nose is pointier on the left as in the example posted by @Ancient Aussie; the chin and the neck is thicker on the left; the profile looks more worn; and the asymmetrical legend looks comfortable. The legend on the right is clear, standing high and the portrait perfectly centered that it looks sort of strange after so many years But while the one the left looks more real and more desirable to this uneducated unpracticed ancient eye my convoluted thinking is that the left is probably forged. (A little later).... Oh! The reverse of the coins are below. I just saw that. But I'm going to stay with my decision that the left is probably forged.
Letters on the left one look softer with flat tops. Very hard to tell from the photos. Both could be good or both could be good fakes. Would have to look for die matches with museum collections but they could still be transfer dies. I guess the left one is fake.
I see what look like flow lines on the right one. That could indicate it was struck vs none on the left one. I would vote left is fake. Do you know one is fake? I assume you will tell us, please.
I too am no expert. While the surface on the left coin looks pockmarked, the coin on the right with the nice planchet flaw on the rim tells my gut: STRUCK COUNTERFEIT. Usually, one side of a counterfeit is better executed (has less bad characteristics and style) than the other. I suspect this is such a coin and that's why the OP did not post the reverse as then our determination would have been easier. Nevermind, LOL I see the reverses are posted. Now the coin on the left really looks bad - corrosion, figure; yet I'll stick to my original GUESS.
Given only the images, and no empirical data like weight, I would not spend money on either coin. They both have suspicious diagnostics. I would need to examine them in hand to say for certain either way.
I too would want to examine in hand before purchasing. I am suspicious of the right example. The fields don't look right based upon the image. In hand is the only way to look. I once was asked to examine 20+ ancients by a dealer and the whole lot was fake. Well done fakes, but fake modern concoctions. A large group can be deceptive in that they look ok by the sheer number which makes them all look good to the casual collector.
The right one is a forgery, as many noticed, the left one is not in a good condition...mais authenic. Now here is my favourite Vitellius:
My first instinct was that the coin on the right was a counterfeit, but I wasn't sure why I thought so until I had a chance to stare at it for a while. The flan looks too flat. The field on the obverse looks so flat that it seems unnatural. I'm told that this flatness can be due to a forgery being pressed in a modern tool-and-die machine, whereas a struck flan is unlikely to have such a uniform flatness. That's what I think I was subconsciously noticing about this coin.