Wickham is a much more slippery character compared to Darcy. Wickham says all the things everyone wants to hear and is thought to be very well mannered and charming. But, he is actually a liar (about his station in life and his relationships with the Darcys) and not a gentleman. This is shown by his willingness to disgrace Lydia and the Bennets by running away with Lydia and refusing to marry her unless his debts are paid for. He rarely has money and is a gambler.
Darcy on the other hand, is very disagreeable in his speech, he is thought to be ill mannered and overly proud. But, he is actually kind and a gentleman. This is shown when he anonymously settles Wickham's debts to save Lydia's reputation.