Explain the pun of the title. Who is being Earnest in this play? Do Gwendolen and Cecily prefer having husbands names Ernest to having earnest husbands?

"Earnest" means honest and truthful. No one in this book is either of those! Everyone is either superficial like Lady Brackness, or full of deceit like Jack and Algernon. The title is a play on words--both being earnest (honest) and being Earnest, i.e. having that name--as if a name makes any real difference. Hilarious!