If the characters were similar, we would have no conflict or fun, now would we :-)?
There are similarities between the characters, yes, but what makes the play interesting are the differences between them. The couples are particularly interesting. Hermia and Helena are quite different. Hermia is the pretty, proper, desired female. She much more attractive than Helena and holds the attention of both Demetrius and Lysander; however, she loves only Lysander. Helena is the not-so-attractive, loose-lipped, vindictive and manipulative female. She is rather awkward and tactless. She loves Demetrius, but he does not love her (at the beginning of the play).
Demetrius and Lysander are also interesting. Lysander is the "good guy" who has noble intentions (for the most part) with Hermia and who truly loves her and wants to marry her. He is proper, polite, and a good suitor. Demetrius, on the other hand, is a cad, a "player." He is also interested in Hermia and wants to marry her, but he sleeps around and is flirtatious with other women. He is self-centered and vain.
The fact that the two "bad" characters (Demetrius and Helena) and the two "good" characters (Hermia and Lysander) end up together is all a part of Shakespeare's plan. In his comedies, all end up happily with the ones they love.
No wonder you're having a problem with this question.
I would argue that Lysander and Demetrius are, for all intents and purposes, the same character in two bodies. They do nothing separately, aside from whom they love.
Helena and Hestia have differences, and certainly one is more interesting to play than the other, but again, these four characters could be staged by two actors.
Among the faeries and royalty, it is often shown that Oberon and Titania are the same as Theseus and Hippolyta respectively, since they are regal and perhaps perfect, and since their follies rather carelessly affect the underlings.
The Puck, of course, stands entirely on his own as the character that ties the two worlds (human and faerie) together.
I don't think that the characters are really similiar. Yes, there are similarities but they perceive differently.
For example, to me, Lysander is a loyal and more of a gentleman when it comes to treating ladies. Demetrius on the other hand does not shows the basic courtesy a gentleman should have escpecially when he threatens to "leave [Helena] to the mercy of the wild beasts" However, there is no doubt a hint of similarity when they challenge each other for the one they love.
Hermia and Helena are probably one of the most contrasting characters. Hermia is more rash yet she is rational and preserves her woman dignity for example when she rejects Lysander offer to lie with her. Helena is another story. She is a submissive character to the point that she is willing to degrades herself for Demetrius.
However, in terms of the Theseus, Hippolyta and Oberon, Titania, they are more similar in some ways than other