Both Hercule Poirot and Sherlock Holmes are renowned detectives. Even there natures are somewhat similar in that they are both egotistical, and reticent about their discoveries till the last minute (Poirot more so than Sherlock), but in their detection methods I found a big difference. Poirot is forever about the 'grey cells' and arranging 'the ideas' with 'order and method'. Physically gallivanting about on foot and searching for clues is solely Hastings' passion and something Poirot never deems necessary. It is not so for Sherlock Holmes. He examines and looks at every footprint, searchs in every nook and cranny and for every single physical piece of evidence at the scene of a crime. Poirot usually leaves this to the detective assigned to the case. But to Holmes this is important. Nevertheless, both men are geniuses who know the art of deduction.
Hercule Poirot is the type to recline in his chair and fit together the pieces of the puzzle. All he needs is some quiet time to organize his thoughts. Sherlock Holmes, to a certain extent, is the same. But as I said before, his detection is more scientific. I don't mean to stress his scientific approach because he was not at all scientific - only as far as comparison goes, he is more scientific than Poirot.
As for physical characteristics, who doesn't know of Poirot's egg shaped head, and his famous moustache? He is not at all a handsome man, but then he plays on that and his insignificance allows him to be taken non-seriously, tricking the criminal into letting down his guard. Sherlock Holmes is decidedly handsome (I think Robert Downey Jr. attests that fact!) and doesn't have the advantage of fooling people into revealing their secrets. Nevertheless, this doesn't keep him back and he is more than enough of a detective to compete with Hercule Poirot.
Then, we also have the styles of the two authors. Conan Doyle likes to reveal the mystery as we move along. That is, we are slowly shown and have it explained to us. At least that was the way it was in The Hound of the Baskervilles. Agatha Christie, on the other hand, creates a sort of atmosphere in which we have all the facts - but are led to look another way. The mystery is only revealed in a gathering at the end of the novel. This atmosphere is detectable on reading the book for a second time. You then begin to see how each fact was presented to us from the beginning, and how we missed it.
Wait till next time to read my opinions on Irene Adler and Countess Vera Rosakoff. So far, I haven't had a chance to read an Irene Adler story. Look for my later comparisons as I read more Sherlock Holmes.