They very much exemplify certain characteristics of society, which were the very characteristics Oscar Wilde detested tremendously:
Algernon- Represents the dandy living above his means, appearing to be respectable, and being treated as so (rubbing shoulders with society) simply because he was born to the upper classes. His eating habits represent greed (which was rampant in Victorian society, as well as the hypocrisy of denying it) and his relationship with Jack/John/Earnest was quite shallow, and entirely convenient. Victorians are thought to be just as superficial, with great "holier than thou" attitudes, and tremendously classist and elitist. He leads a double life (like many Victorian husbands and wives alike) by visiting his fake friend Bunbury whenever he wants to escape to the country
Jack is no different than Algernon, except that he is more responsible with his money but then again, he also leads a double life by visiting his fake sick brother "Earnest", when he wants to escape to the city.
Lady Bracknell,however, takes the cake- She is THE epitome of the upper class, elitist, snobby, fake, shallow and money-hungry "upper crust" that Wilde belonged to, yet, completely criticized and mocked. That is why he always creates a character such as Lady Bracknell in most of his plays.
In all, the story does epitomize the Victorian city life and country life, accentuating in how the characters in either place still carry the same weaknesses that society encourages them to carry.