Well, I checked the first comic again. The best face shot is in the last panel, but he's in a pretty awkward pose, and the speech bubbles will get in the way if we crop them (if we don't, they will be useless without context). I chose the first panel because it's self-sufficient and pretty funny by itself.
On a side note, Poirot's pic makes my OCD conflict itself: It's 256 pixels wide, when I stuck to 250, but uploading a whole new pic and cluttering TV Tropes' server is even worse.
Also, I hope we'll get another Poirot's comic, because a mask shot is not the best pic, even though it's the only one we have.